Every population of mankind creates their own habit. Such habit are derived from the art of life survival and to avoid extinction through reproduction. Such population highly likely has their own distinctive culture, as a part of identity and signature of existence.
Cultural faux pas often happens when an individual travels into another circle, and meets different way of living, or different habit. Cultural faux pas may stimulate conflicts or coalition depend of how circumtances happened.
A slip or blunder in etiquette, manners, or conduct; an embarrassing social blunder or indiscretion, is a disastrous moment to be awaited, by any warlord or politician, when they engage in a battlefield or diplomacy. Taking advantage from a faux pas is a common thingy.
So, how do you know the moment meet friends or foes? Wait their reaction at the moment of cultural faux pas, that simple.