Sack Flapping 

The sound your ballsack makes when pounding a tight slizz from behind; a good sack flap goes to a beat and makes a soft thumping noise... & can lead to minor bruising and irritation of the stomach region of the partner whos tight slizz or smelly balloon knot is being ravaged

Kelly: "Whats that on your stomach?"
Sara: "I had a good Sack flapping last night"
Kelly: "Oh i got sack flapped last wednesday; and his beanbag bruised the hell out of my tummy "

Sack Flapping by Capel & Droughton November 19, 2011

flip flaping the jacking sack 

Choking the chiken or any form of self plesure or masturbation involving your hand, lube ,and your favorite playboy mag.

i'm flip flaping the jacking sack.

flip flap the jacking sack

flip flaping the jacking sack by wakety sacety May 8, 2009