Airborne andy
This involves first waiting until the victims back is turned. You must then pull down your trousers and underwear, completely exposing your cock and balls. You then wait for the victim to turn around, and perfectly time a vertical jump, to ensure that you are completely airborne when their eyes first meet your tackle. The jump has a sort of 'zero gravity' effect on the male genitals, causing them to float up from their normal position, thus creating a new, unexpected and interesting way of pranking your victim.
I just turned around and Jonny hit me with an airborne andy!