Two teams of people (in even numbers) line up on each side of a long table.

Each person has a plastic cup in front of them, filled about 1/6 with beer.

The two people facing each other on one end of the table begin the game by drinking at the same time, placing their empty cup face down on the table with the lid hanging slightly over the edge, and flipping the cup over using their finger.

When the player successfully flips their cup so that it's face up, the player to the right of them drinks and flips and so on ...

The team that flips all their cups over first wins. Usually people play best of 11 or 15 so you can get pretty wasted.