The act of pelvic thrusting in your underwear to make your male genitalia flop from your belly button to your gooch area. The illusion is similar to the sight of a frog jumping around in a bag.
Tim: Hey Paul, come here you gotta see this.
Paul: Better not be a Frog in a Bag, I don't wanna see your sack flopping around anymore.
Paul: Better not be a Frog in a Bag, I don't wanna see your sack flopping around anymore.
by PaulAsh69 November 8, 2012