This game is similar to the game "Libya" but more violent. You can play with more people and of course more beers.
You fashion the cups in a pyramid with a base as large as of however drunk you want to be. When Team 1 lands a ball in a full cup, Team 2 must drink it. However, unlike "Libya", do not remove the cup. Drink it and place it back where it was. Now if Team 1 lands the ball in any empty cup, Team 1 must drink a penalty from beer not on the table.
Keep firing until all the cups on one team have been drained. Once this happens, the losing team (the one with no full cups left) must drink the remaining cups from the other team. Again, very simple.