A penis cake is, as the phrase implies, a cake that's either shaped like a penis or has one built on a regular cake. The penis stands vertically, and a small tube, like the ones used in fish tank filters, is run through the shaft and out the side of the cake. The end is connected to a
turkey baster filled with milk, which should be concealed in some way to avoid ruining the surprise.
When the unsuspecting birthday person goes to blow out the candles, their friends slam down on the
turkey baster and give them a
birthday money shot.