How common it is for the average Catholic, even a conscientious one, to overlook the implications of scandal. Usually scandal is looked at only as the sin of another person done publicly. And, a Catholic may think nothing either of listening to it, reading it, or passing the news on to others, thinking to themselves, "Well, I am not revealing a private sin; this is already a public matter, so I am not ruining anyone's reputation!" As far as the culprit's reputation is concerned this may be so, but scandal is entirely another matter for consideration. A person's reputation is only one side of the coin.
A Catholic must worry not only about GIVING scandal, he must also worry about TAKING scandal! The Church teaches that anyone who TAKES scandal (whether it is given or not) is guilty of sin. It is common to hear of Catholics who TAKE scandal from their priest and stop going to the sacraments just because they think that the priest had offended them on the pulpit, or in person. Or, for instance, if the priest seems too preoccupied with money for the Church, or has created a parochial policy which makes things especially difficult for that particular parishioner. Whether the priest has given scandal or not, a person would be offending God by TAKING scandal.
And so, Catholics must be always on their guard not only to give a good and prudent example to others in order to avoid GIVING scandal, but they must also be on their guard to avoid being adversely affected by the actions of others without letting it interfere with the spiritual duties to themselves, to their neighbor, and above all to God. The following quotes from various Catholic sources will give the details of the Church's teaching on SCANDAL.

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From "A Catholic Dictionary", Attwater (1954)

SCANDAL (From the Greek for - Stumbling block). Active scandal is occasioning the sin of another by any word or deed which is or appears to be evil; passive scandal is the sin so committed by the other. The former is a sin against charity, mortal if the other is thereby put into a proximate occasion of mortal sin; should the other's sin be intended and not merely foreseen, that sin also is committed by the giver of scandal. An action which, though good, appears evil to the onlookers, should not be performed unless grave inconvenience would result from its omission. Scandal caused in another by a good action on account of his evil dispositions is "Pharisaical," and need not be considered.

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From "Catholic Controversy", St. Francis de Sales

"All comes back to the saying of the prophet, "Destruction is thy own, O Israel!" Our Lord was the true Saviour who came to enlighten every man and to be a light unto the revelation of the Gentiles, and the glory of Israel; whereas Israel takes hereby occasion of ignominy. Is not this a great misfortune? And when it is said that he is set for the ruin of many, this must be understood as to the actual event, not as to the intention of the divine Majesty. As the Tree of the knowledge of good and evil had no virtue to teach Adam either good or evil, though the event gave it this name, because Adam by taking the fruit experienced the evil which his disobedience caused him. The Son of God came for peace and benediction, and not for evil to men; unless some madman would dare to cast up to our Lord his holy Word: "Woe to that man through whom scandal cometh", and would condemn him by his own law to have a millstone tied about his neck and be cast into the depths of the sea. Let us then confess that not one of us men is scandalized save by his own fault. This is what I undertake to prove by force of argument. O my God, my Saviour, purify my spirit; make this your word distill sweetly into the hearts of my readers, as a sacred dew, to cool the ardor of the passions which they may have, and they shall see how true, in you, and in the Church your Spouse, is that which you have said.
It was, I think, that great facility which men find for taking scandal, which made Our Lord say that "scandals needs must come", or, as St. Matthew says, "Woe to the world because of scandals"; for if men take occasion of their harm from the sovereign good itself, how could there not be scandals in a world where there are so many evils?
Now there are three sorts of scandals, and all three very evil in their nature, but unequally so. There is a scandal which our learned theologians call "active". And this is a bad action which gives to another an occasion of wrongdoing, and the person who does this action is justly called scandalous. The two other sorts of scandal are called "passive" scandals, some of them passive scandals "ab extrinseco", others "ab intrinseco". For of persons who are scandalized, some are so by the bad actions of another, and receive the active scandal, letting their wills be affected by the scandal; but some are so by their own malice, and, having otherwise no occasion, build and fabricate them in their own brain, and scandalize themselves with a scandal which is all of their own making. He who scandalizes another fails in charity towards his neighbor, he who scandalizes himself fails in charity towards himself, who is scandalized by another is wanting in strength and firmness. The first is scandalous, the second scandalous and scandalized, the third scandalized only. The first scandal is called "datum", given, the second "acceptum", taken, the third "receptum", received. The first passes the third in evil, and the second so much passes the first that it contains first and second, being active and passive both together, as the murdering and destroying oneself is a cruelty more against nature than the killing another. All these kinds of scandal abound in the world, and one sees nothing so plentiful as scandal: it is the principal trade of the devil; whence Our Lord said, "Woe to the world because of scandals." But scandal taken without occasion holds the chief place by every right, [being] the most frequent, the most dangerous, and the most injurious.
And it is of this alone that Our Lord is the object in souls which are given up as a prey to iniquity. But a little patience: Our Lord cannot be scandalous for all in him is sovereignly good; nor scandalized, for he is sovereignly powerful and wise; - how then can it happen that one should be scandalized in him, and that he should be set for the ruin of many? It would be a horrible blasphemy to attribute our evil to his Majesty. "He wishes that every one should be saved and should come to the knowledge of his truth." He would have no one perish. Our destruction is from ourselves, and our "help" from his divine goodness. Our Lord then does not scandalize us, nor does his holy Word, but we are scandalized in him, which is the proper way of speaking in this point, as himself teaches, saying: "Blessed is he that shall not be scandalized in me." And when it is said that he has been set for the ruin of many, we must find this verified in the event, which was that many were ruined on account of him, not in the intention of the supreme goodness, which had only sent him as a light for the revelation of the Gentiles and for the glory of Israel. But if there are men who would say the contrary, they have nothing left [as I have said] but to curse their Saviour with his own words: "Woe to him by whom scandal cometh."
I beseech you, let us look in ourselves for the cause of our vices and sins. Our will is the only source of them. Our mother Eve indeed tried to throw the blame on the serpent, and her husband to throw it on her, but the excuse was not valid. They would have done better to say the honest "peccavi", as David did, whose sin was immediately forgiven.
I have said all this, gentlemen, to make known to you whence comes this great dissension of wills in matter of religion, which we see amongst those who in their mouths make profession of Christianity. This is the principal and sovereign scandal of the world, and, in comparison with the others, it alone deserves the name of scandal, and it seems to be almost exactly the same thing when Our Lord says it is necessary that scandals come, and St. Paul says that "there must be heresies;" for this scandal changes with time, and, like a violent movement, gradually grows weaker in its evilness. In those Christians who begin the division and this civil war, heresy is a scandal simply "taken", passive "ab intrinseco", and there is no evil in the heresiarch save such as is entirely in his own will; no one has part in this but himself. The scandal of the first whom he seduces already begins to be divided; - but unequally, for the heresiarch has his share therein on account of his solicitation, the seduced have a share as much the greater as they have had less occasion of following him. Their heresy having taken root, those who are born of heretical parents among the heretics have ever less share in the fault: still neither these nor those come to be without considerable fault of their own, and particularly persons of this age, who are almost all in purely passive scandal. For the Scripture which they handle, the neighborhood of true Christians, the marks which they see in the true Church, take from them all proper excuse; so that the Church from whom they are separated can put before them the words of her Lord: "Search the Scriptures, for you think in them to have life everlasting: and the same are they that give testimony of me." : "The works that I do in the name of my Father, they give testimony of me."
Now I have said that their scandal is purely or almost purely passive. For it is well known that the occasion they pretend to have for their division and departure is the error, the ignorance, the idolatry, which they aver to be in the Church they have abandoned, while it is a thing perfectly certain that the Church in her general body cannot be scandalous, or scandalized, being like her Lord, who communicates to her by grace and particular assistance what is proper to him by nature: for being her Head he guides her feet in the right way. The Church is his mystical body, and therefore he takes as his own the honor and the dishonor that are given to her ; so it cannot be said that she gives, takes, or receives any scandal. Those then who are scandalized in her do all the wrong and have all the fault: their scandal has no other subject than their own malice, which keeps ever tickling them to make them laugh in their iniquities."

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From "Catholic Encyclopedia", (1913) Vol. XIII

Scandal. - This article will treat:
I. THE NOTION OF SCANDAL;
II. ITS DIVISIONS;
III. ITS MALICE;
IV. CASES IN WHICH THE SIN OF SCANDAL OCCURS.

I. NOTION OF SCANDAL.
- According to St. Thomas (II-II, Q. 43, art. 1) scandal is a word or action evil in itself, which occasions another's spiritual ruin. It is a word or action, that is either an external act-for an internal act can have no influence on the conduct of another-or the omission of an external act, because to omit what one should do is equivalent to doing what is forbidden; it must be evil in itself, or in appearance; this is the interpretation of the words of St. Thomas: "minus rectum". It is not the physical cause of a neighbor's sin, but only the moral cause, or occasion; further, this moral causality may be understood in a strict sense, as when one orders, requests, or advises another to commit the sin (this is strictly inductive scandal, which some call co-operation in a broad sense), or in a large sense, as when a person without being directly concerned in the sin nevertheless exercises a certain influence on the sin of his neighbor, e.g. by committing such a sin in his presence (this is inductive scandal in a broad sense). For scandal to exist it is therefore essential and sufficient, with regard to the nature of the act and the circumstances under which it takes place, that it be of a nature to induce sin in another; consequently it is not necessary that the neighbor should actually fall into sin; and on the other hand, for scandal strictly so-called, it is not enough that a neighbor take occasion to do evil from a word or action which is not a subject of scandal and exercises no influence on his action; it must be a cause of spiritual ruin, that is of sin, consequently that is not scandal which merely dissuades the neighbor from a more perfect act, as for instance, prayer, the practice of the Evangelical virtues, the more frequent use of the sacraments, etc. Still less can that be considered scandal, which only arouses comment, indignation, horror etc., for instance blasphemy committed in the presence of a priest or of a religious; it is true that the act arouses indignation and in common parlance it is often called scandalous, but this way of speaking is inaccurate, and in strictly theological terminology it is not the sin of scandal. Hence scandal is in itself an evil act, at least in appearance, and as such it exercises on the will of another an influence more or less great which induces to sin. Furthermore, when the action from which another takes occasion of sin is not bad, either in itself or in appearance, it may violate charity (see below), but strictly speaking it is not the sin of scandal. However, some authorities understanding the word scandal in a wider sense include in it this case.

II. DIVISIONS.
(1) Scandal is divided into active and passive. Active scandal is that which has been defined above; passive scandal is the sin which another commits in consequence of active scandal. Passive scandal is called scandal given (scandalum datum), when the act of the scandalizer is of a nature to occasion it; and scandal received (acceptum), when the action of the one who scandalizes is due solely to ignorance or weakness-this is scandal of the weak (infirmorum), - or to malice and evil inclinations-this is pharisaical scandal, which was that of the Pharisees with regard to the words and actions of Christ.
(2) Active scandal is direct when he who commits it has the intention of inducing another to sin; such is the sin of one who solicits another to the crime of adultery, theft etc. If one prevails upon another to commit the sin not only because of an advantage or pleasure believed to accrue therefrom but chiefly because of the sin itself, because it is an offence to God or the ruin of a neighbor's soul, direct scandal is called by the expressive name of diabolical scandal. On the other hand scandal is only indirect when without the intention to cause another to fall into sin we say a word or perform a deed which is for him an occasion of sin.

III. MALICE.
(1) That active scandal is a mortal sin Christ Himself has taught (Matt., xviii, 6 sqq.) and reason makes evident. If charity obliges us to assist our neighbor's temporal and spiritual necessities (see ALMS; CORRECTION) it obliges us still more strongly not to be to him a cause of sin or spiritual ruin. Hence it follows that every sin of scandal is contrary to charity.
(2)Moreover direct scandal is obviously contrary to the virtue against which another is induced to sin; in fact every virtue forbids not only its violation by ourselves but also that we should desire its violation by another.
(3) Indirect scandal is also contrary to charity (see above); but is it also opposed to the virtue violated by another? St. Alphonsus answers in the affirmative- others, and this seems the true opinion, deny this. In fact no one has hitherto proved this species of malice, and those who admit it are not consistent with themselves, for they should also maintain, which no one does, that anyone who is indirectly the cause of an injustice by another is also bound to restitution; what is true of justice should hold good for the other virtues.

IV. The question remains:
WHEN IS THERE A SIN OF SCANDAL?
For it is obvious that not all who are the occasion of sin to others are thereby guilty.
(1) As a general rule the sin of scandal exists when one directly induces another to do a thing which he cannot do without sin, either formal or material, e.g. by soliciting a person to perjury, drunkenness, sins of the flesh, etc., even though the person induced to this act is habitually or at the time disposed to commit it. It is otherwise when the thing we ask is good or indifferent; this may be done without scandal and without sin, when there is a just cause or serious reason for asking it; even though one foresees that the other will probably sin in granting it; thus for the common weal a judge may demand an oath even from those who will probably commit perjury; one who has need of money and who cannot find anyone who will lend to him may have recourse to a usurer although he foresees that the latter will exact exorbitant and unjust interest, etc. The thing asked must be without sin either formal or material because it is not allowed to profit by the ignorance of another to induce him to commit what is forbidden; to cause a child to utter blasphemies, to induce someone who is unaware of the precept of the Church to eat flesh on a fast day, and so on. In fact in all these cases the sin is to be ascribed to the person, who endeavors to cause it. This is the general rule, but here the question arises, may one advise another bent on committing a great crime to be satisfied instead with doing something less evil? This question is much discussed, but the opinion which considers such a course justifiable is probable and may be followed in practice. In fact the advice thus given is not properly speaking advice to do evil but to do a lesser evil or rather not to do the greater evil which a man intends to commit; therefore some writers exact that the words or circumstances must demonstrate that one advises the evil solely as the lesser evil; others, however, consider it sufficient that such be the intention, even when not made manifest, of the person who gives the advice. Nevertheless, if a man had decided to do an injury to a certain person one could not - unless in exceptional circumstances -induce him to do a lesser injury to any other person.
(2) He is guilty of the sin of scandal who without positively pledging or inducing to sin nevertheless performs an act evil in itself which will be an occasion of sin to another. The same must be said when the act is evil only in appearance, unless there be sufficient reason to act and to permit the fault of another. Thus those who blaspheme before others when they foresee that their example will cause the latter to blaspheme are guilty of scandal; so also those who attack religion or morals, hold immoral conversation, sing immoral songs or (by their behavior, dress, writings etc.) offend against the laws of decency and modesty, when they foresee, as is usual, that those who see hear or read will be impelled to sin.
(3) To prevent another's sin one may even be bound to forego an act which is sinful neither in itself nor in appearance, but which is nevertheless the occasion of sin to an-other, unless there be sufficient reason to act otherwise. It has already been shown that when there is a just cause, we may ask of another a thing which he can do without sin although we may foresee that he will not do it without fault. Likewise we are not bound to be disturbed by pharisaical scandal, which may follow an action we perform; but we must avoid scandalizing the weak if we can do so easily. The application of these Principles depends on concrete circumstances , which vary with each case; however, the following general rules may be given:
(a) To prevent scandalizing another we must never transgress the negative precepts of the natural law, nor its positive precepts in cases where they truly bind; thus it is not permitted to lie to prevent a mortal sin, neither can one neglect receiving baptism to avoid the blasphemies of one's parents.
(b) It is not permitted to pass over any precept whatever in order to prevent pharisaical scandal, but we may and even should, in special cases and for one or two occasions, pass over a precept whether Divine or human, to avoid scandalizing the weak.
(3) We should, to avoid scandal, forego good or indifferent works which are not of precept, if we can do so without great inconvenience. (4) Finally, to prevent the scandal of the weak we are sometimes obliged to sacrifice some temporal good of less importance, but we are not bound to do this when the goods are of greater importance.