dorkwave
Dorkwave (dôrk’-wav) 
Origin – dork (dôrk)n vulgar slang for the penis +  wav (wav) v. to make a signal with an up-and-down or back-and-forth movement of the hand or an object held in the hand

1. Wagging one's own penis after micturating to release the last few drops of urine before zipping up one's trousers.

2. The act of grasping one's own (or other's) penis whilst holding the testes with the other hand (thereby repressing them from movement), and presenting it forcefully with an undulating motion at another's face, or at an anonymous passerby. If in an aroused state, bouncing upon one's forehead is also popular.
Gerald needs to perfect his dorkwave, he's always got a wet spot on the front of his trousers when he comes back from the bathroom.

Some man with a frightening look on his face just gave me a dorkwave outside of your cubicle.