I know two great drinking games that make everything else suggested so far seem tame:
Marshmallow Run:
You need a long room, or a long tent, or a big garden.
Put a pole at one end of the room/tent/garden etc, with a table next to it. On that table, you put a large number of drinks, either strong pints, or triple shots.
At the other end, put another table, with 2 large bowls on it. In one bowl, put jam, and mix in some tiny marshmallows. In the other, put icing sugar, and mix in more marshmallows.
The game: Start with six contestants and about thirty other people to egg them on, throw things and judge in/out.
Contestants line up by the pole. They have to either down the pint, or drink the shot. Spillage counts as a fail, and they're out. They then run around the pole three times, without touching it, run to the other end of the room to the table. They must then get a marshmallow [or other] out of first the jam, and then the sugar, without using their hands. They have 3 tries, or they're out.
They must then run back the pole, run around it three times, drink another drink, run around the pole again, and go back to the bowls. Keep going until everyone has either fallen over, spilled/failed to drink their drink, or failed with the marshmallows. Last person 'in' wins. Shoving, kicking, mauling and biting are all acceptable ways to make sure that you are the first person to get to the jam and sugar bowls.
It works even better if the contestants are men in stiletto heels.
Holding onto the pole or leaning on the tables is an automatic 'out'
My Ass is on Fire!
Build a big bonfire. By big, I mean at least four feet in diameter.
Once its built up suitable big and roaring, get a piece of really wet plyboard and put it in the middle of the fire, flat, like a stage. You’ll need quite a few of these by the way!
The person nominated to go first needs to jump into the middle of the fire and stand still. They then have to down a set amount of drink, and jump out of the fire, without setting themselves alight.
The first person is lucky- they have a much lower chance of being set on fire than the second person, who has to jump in after and also down a drink before they get out.
You get ‘out’ by setting fire to some part of yourself, or by chickening out and failing to down your drink. You cannot change the piece of plyboard until all the people taking part have had a turn. For that reason, I wouldn’t recommend more than four players.
t:
