In beirut, when team members make shots into the same cup in one turn, the opposing team has to drink every cup that is touching that cup in addition to the cup the shots were made in to. In addition to that, the players that just shot get to take another turn.
If the game is a more than two players, the number of shots made into a cup for a clusterfuck must be determined. For instance, if the game is 4 on 4, 3 shots into the same cup may qualify as a clusterfuck.
That beirut game was close until we clusterfucked you, then you were screwed.