What is decorum? It is to avoid what is objectionable in the eyes of others and has the function of doing just that.

-Abhidharmasamuccaya

The difference between self-respect and decorum  is that, despite their similarity in avoiding evil actions, when the chance of doing evil actions is close at hand, self-respect means to refrain from evil actions in view of the consideration, "This is no part of mine." Decorum means to refrain from evil action by having made others the norm in view of the consideration, "It is not appropriate to do so because others will despise me." The primary realm of restraint is the fear that one's guru and teacher and other people deserving respect would be annoyed.

The statement that the function of self-respect and decorum is the basis for refraining from evil action properly emphasizes the necessity of these two in refraining from evil action by body, speech and mind, because if self-respect and decorum are not there, one is incapable of restraining any evil action. If there is no fear about the result that might come from one's own action and no fear that the guru, teacher, and others deserving respect would be annoyed, there is no chance that evil behavior will ever stop.