As a relatively new player I do find losses extremely upsetting very often, unless I've only lost by a few points against someone at the same level as me; I guess I have some learning to do :)
Not really, I've seen amateur 1-2 Dan insulting the other player before leaving a game (online), or just trolling to piss off the other player. People get really childish in Go because it's hard to accept defeat in this game.