Here's something else: When students think they know more about the language or teaching than I do! It's not that I don't make mistakes, or am never wrong... that's not the problem. I'll be the first to admit that I don't know, am not sure, or was incorrect about a language point. But when a student remains adamant that he knows the language better (or how to teach better), even when faced with expert opinions such as textbooks, grammar books, dictionaries, etc., it gets under my skin.
