I avoid multi-player games for this reason. I'm a quitter. I'm not saying I'm a sore loser, but if I just feel like I need to stand up and walk around, or worse, get pissed off at the game, I see no reason to continue playing. It starts to hurt to play if I'm bored or enraged.
I just started up a Freelancer server, and my brother loves to play it. There was twice now that he was headed for me to team up, but I was on some mission that I just blew up without much warning, so I was too pissed to keep playing.
Dont' get me wrong. I'm not an angry person, but if things put me over the anger threshold, then playing more is the last thing I should be doing.