A reference to doggy style gay sex where the pitcher's abnormally long balls (bean bag) swing in a pendulum like manner and strike the underside of the catcher's fleshy meat sac (bean bag).
Gay Guy 1: "oh my cubes are so bruised from that vicious game of bean bag tag last night."
Gay Guy 2: "did you play with joe again?"
Gay Guy 1: "yea, when he gets his momentum going his nuts are like two cannonballs in a pair of nylons!"
Gay Guy 2: "Yea i know what that is like... his flesh bag is a wrecking ball designed for crushing man bags."