When one party hits a second party's genitals with the back of their opened hand. They must also say, "Gershwin," for it to count.
Try it on a friend today...or better yet and unsuspecting stranger.
Tim and Jon are singing in chorus when Snyder sneaks up behind them. Snyder says, "Hey guys." They turn. SLAP! "Gershwin!"
Garrett Hidey; Stupid!
"Looks at me with his crooked smile while Gershwin plays." Moe. - New York City