One thing that tends to crop up in rpgs groups eventually is the idea of Player vs. Player conflict. Assuming that the group doesn’t consist of people who figure that games are like museum tours where everyone holds hands and walks the same path all the time, there’s bound to be some form of conflict of interest that will happen eventually.
Commonly termed as Player vs. Player, you may get situations where characters are already at the point of physical combat and trying to kill each other to resolve things. Some groups like this and others… well, others fall apart when players start taking things personally.
A little inter-character conflict is a good thing, as it allows players to pretty much further define their characters. However, once tempers flare in real life, this gets really messy. So, what’s a GM to do?
This is where the idea of “plays well with others” comes in. GMs are, aside from the guy who knows the rules, is also often thrust into an unofficial leadership position. Players expect him to take charge when things like these come out and you should be careful that what happens in the game, stays in the game rather than becoming a real world grudge.
I’ve only seen a full-on player confrontation happen once in a game I ran before and it wasn’t pretty. Slinging insults and then eventually the fistfight. Had to break it up and kick both players out of the game.