The rules are quite simple; potentially high buzz factor. As usual the basic supplies are people and beer.
Each person starts with a full glass/mug/stein/tankard/cup of beer. Any beer will do, but preferably something quite inexpensive.
All players start drinking at the same time. To signal that you have finished you hold the glass *upside-down* above your head; if anyone does so then the other players must do the same whether or not they have finished drinking.
IMPORTANT NOTE: It isn't required that you actually drink the beer before claiming to have won; the winner is the first person to invert their glass above their head regardless of whether they actually drank the contents.