PloxBox, I'm not sure if this is the kind of game that you were thinking of, but there's a TF2 game which is called (not sure if this is the official name or not, but it's what I'll be calling it) "Double Agent.". In the game, there are two normal teams(the number of players doesn't matter) and they play normally. However, every round, the person running this event will randomly select one player from each team and will secretly tell them that they are the double agents. Their goal is to make their team lose, but to not be caught in the process. At the end of every round, the double agent of the winning team will be eliminated. The losing team will have a vote on who they believe the double agent for their team is, and the person who received the most votes will also be eliminated, regardless if he/she was the actual double agent or not. This goes on until there are only 2 people remaining, but can also simply end at 4 to simplify things.
Or, if you're looking for a more forum-like thing to do, you can have "Name/Describe this hat" contests, where people have to, well, name/describe a given hat/weapon.