A phrase that
people use when they want to be considered "fashionably
late" but are actually on time for the event in question.
People who say they are "fashionably on time" are usually either joking or have an inflated sense of self-importance.
Guest 1: I'm here; I guess I'm fashionably
late.
Guest 2: Actually, you're not
late. The
party is starting right now.
Guest 1: Oh, well, in that case...I must be...fashionably on time!