Say that I'm having lunch with my buddy outside, and my boss comes over and starts talking to me. Obviously, with my boss, I'll talk with proper keigo and stuff. But in front of my boss, am I allowed to talk directly to my buddy with full-blown tameguchi, or is that considered impolite?
For example, say my buddy was teasing me in front of my boss with something like "____は相変わらず不器用ですか" ("Is _____ still clumsy as always?"). Am I allowed to retort at my buddy with things like "何いってんだお前" (the hell you on about) and "うっせお前" (shut your ass), or would it be considered rude to talk like that in front of my boss, even if the language isn't directed at my boss?