This is a two part move. First, tuck your junk under and back and hold your junk back with your butt cheeks. At this point your slingshot is loaded...now just to find a victim. It's best if you find someone's face. Release the tension on your butt cheeks slingshoting your junk forward. Can be an insult or an offering.
I gave that bitch the "Malaysian Slingshot." Damn near took her eye out.