I tend to think that those are pretentious rather than insulting, because it's so obvious that I'm not French or Italian. However, real French or Italian people are VERY unlikely to go around greeting people in their own language unless they know for sure that the other person speaks that language and is comfortable doing so. For example, I know four languages fluently but I usually stick to English all the way, just because going "Bonjour!" at someone reeks of "let me show off my pathetic, limited vocabulary in an attempt to impress you!".