On one game of Halo 3 on sandtrap, we had some people randomly start insulting me and another teamate. So everyone else on our team suddenly opens up on the flamers and start yelling at them until they leave. Now we're losing pretty bad, but then we started working risking their (spartan's) lives to protect injured comrades. The whole time we were socializing about everything, and then we won the match with a few seconds left. It was so awesome, and everyone started adding each other as friends. After that, we played in the same playlist for and hour or two more and it was great.
The worst games are obviously on CoD4...too many to count...teamates killing comrades on hardcore, idiots screaming at people, calling them random names and making fun of their mothers, an entire team camping, starting a game outnumbered and losing but when you get more teamates you start doing better so the enemy host quits the game just to piss people off.