I have a friend who maintains that every game — EVERY game — would be improved with the addition of a traitor mechanic if only we could work out how to implement it.
Pandemic: You win if the others lose. Hands are played closed and no one is allowed to say what cards they have explicitly. Convincing your ‘team’ you can’t help and persuading them to make bad choices is how you win.
Flash Point Fire Rescue: You set the fire. You win if the others loose BUT all deaths, including yours, are permanent. If you are in the building when it collapses, you lose. If you get caught in a fire, you lose. The main team only need to find five civilians to win.
Ticket to Ride: There’s a chance that one of the initial tickets is a traitor card. Instead of getting points in the usual way, you get the points of all the tickets your opponents failed to complete.
7 Wonders: Less of a traitor mechanic, more of a being-an-arse mechanic (most of them are from this point to be honest). Your wonder is all about making other people lose points and there are extra black city cards in the deck to help you.
Terraforming Mars: You get your own special deck with all the attack cards in. You win if after a set number of generations (depending on the number of players) Mars has not been terraformed.
Settlers of Catan: You are the robber. You ALWAYS control where the robber moves and automatically roll a seven on your turn. Instead of building settlements and cities, you steal other people’s. It takes eight points to win.
If you can think of any games to traitor-ise, drop me a note in the comments below.