Taken from Wikipedia:
A faux pas (/ˌfoʊˈpɑː/ plural: faux pas /ˌfoʊˈpɑːz/) is a socially awkward or tactless act, especially one that violates accepted social norms, standard customs, or the rules of etiquette.
The expression faux pas comes from French, where it means "false step", "misstep" (in a physical as well as a figurative sense). It has been used in English for over 300 years.Synonyms in English include gaffe and (social) blunder.
Two buttons ONLY on a paddock cut suit jacket
And of course, it is also proper that the jacket stays buttoned when you are standing, walking (I doubt people would care or you would care if you were running). Unbutton the jacket when you are seated so that you are more comfortable.