In beer pong, otherwise known as beirut, depending on the rules (either 6 cup or 10 cup) you are allowed one or two re-racks, respectively. You call for a re-rack when you have 6, 4, 3, 2 or even 1 cup left for a better formation. You cannot call a re-rack until it is your turn to shoot, and you can't call one if you or your partner shoots. It has to be the very beginning of a turn.
Dude, we have 2 cups left but they're mad far apart. Let's re-rack that shit when we get the balls back.