Backgammon. A pretty tame game, that just gets tamer. Supplies: you and a partner who wants to play Backgammon, the game itself, and some beverage. Low-mid buzz factor, depending on how fierce the competition is.
Play the game as usual. Any time one of your pieces gets sent to the bar, drink. As well, each time you take a piece off the board, drink again. Pretty straightforward. No winners or losers, really; Just drunk backgammon players.