Catch Drinking Game
Get a large mixed group together and go off to some grassy spot. Take a ball or suchlike and as much hooch as you can carry between you. Form a vague largeish circle and stick the booze in the middle, then just throw the ball around (fake throws, misdirection, etc OK) until either
Someone fails to catch it or
Someone throws the ball in a completely crap direction.
The person deemed to have perpetrated (a) or (b) then has to stand still and time the rest of the group for 20 seconds while they run into the middle and drink as much as they can in the time available. The advantage of this game is that people who have some eye-hand coordination or who are just unsportingly sober get brought down to the level of the rest of the group.
You can adapt the rules to any kind of ball game (baseball, cricket etc), but we found that it's best to stick to games which can succesfully be played while everyone's completely smashed.