In the game of beer pong, desperation diamond is a type of rerack only used when the player is losing and needs to sink four more cups. The rerack forms the four cups into the shape of a diamond. In most games of beer pong, you can only only rerack once; therefore you are giving up your rerack privileges early. This rerack is desperate but advantageous in certain situations.
You have one cup left on your side. You're opponent has four cups left on his side. You rerack since time is running out and you need the increase your chances of making cups.