You have a table, and 1 person from each pair is standing at a head of the table. So at first glace it looks like ruit, but you are actually standing ACROSS from your partner. Each person has 4 cups lined in front of them, and each pair has a ping pong ball. The objective is to throw the ball into your partners 4 cups, if you sink one, then your partner drinks it, and plays flip cup with it. Once he flips it, he can shoot on your cups. First team to flip all 8 cups, wins. It is a game of speed, which makes it infinitely better than ruit.
What makes it different is also that the winner drinks more than the loser, usually it's a full beer for each four cups. Plus a game with good players takes about 3 minutes, so more people get to play.