I've never heard of the expression "faux-amis," in English. In French it would mean false friend which would probably mean somebody that pretends to be your friend, but that isn't really. In the study of languages, a "false friend," is something completely different - it is a situation that occurs when a learner sees a word in a language that he is studying that looks extremely similar to a word in his native language, but has a totally different meaning to the meaning in his native language. "Faux-pas," is a French term that we certainly use in English. Its literal meaning is "false step." We use it to mean something that somebody has done which is embarrassing... we usually understand that this embarrassment occurs in a social context - for example saying something stupid in polite company.