So the virtue of modesty (a part of temperance) is to reasonably restrain the less violent human passions.
A person could sin by giving scandal (lead others into sin), either actively or passively, even by an act that is not a sin in itself. So we must avoid scandalizing the weak if we can do so easily.
Did you ever read St. Thomas Aquinas on this issue? I concluded the following after study.
Passive scandal is the sin which another commits in consequence of active scandal. Active scandal can be accidental or direct.
Accidental active scandal:
Accidental active scandal is venial when a venial sin or only appearance of evil scandalizes.
Accidental active scandal is mortal if mortal sin scandalizes another to mortal sin, or if one will not forgo for the sake of the scandalized. (Example: drinking around a known alcoholic.)
Direct active scandal:
Intention of a venial sin leading another into venial sin is then a venial sin.
Intention of a mortal sin leading another into mortal or venial sin is then a mortal sin.
Did you ever read St. Thomas Aquinas on this issue (Summa Theologica, II, II, Question 169. Modesty in the outward apparel, Article 2. Whether the adornment of women is devoid of mortal sin?):
I answer that, As regards the adornment of women, we must bear in mind the general statements made above (Article 1) concerning outward apparel, and also something special, namely that a woman’s apparel may incite men to lust, according to Proverbs 7:10, “Behold a woman meeteth him in harlot’s attire, prepared to deceive souls.”
Nevertheless a woman may use means to please her husband, lest through despising her he fall into adultery. Hence it is written (1 Corinthians 7:34) that the woman “that is married thinketh on the things of the world, how she may please her husband.” Wherefore if a married woman adorn herself in order to please her husband she can do this without sin.
But those women who have no husband nor wish to have one, or who are in a state of life inconsistent with marriage, cannot without sin desire to give lustful pleasure to those men who see them, because this is to incite them to sin. And if indeed they adorn themselves with this intention of provoking others to lust, they sin mortally; whereas if they do so from frivolity, or from vanity for the sake of ostentation, it is not always mortal, but sometimes venial. And the same applies to men in this respect.
newadvent.org/summa/3169.htm
