Balls. When sitting correctly, a mans testes may cover the anus and becoming a 'mud flap'. Also, when two are engaged in intercourse in the missionary position, the mans testes may cover the woman's anus and therefore becoming the woman's 'mud flap'.
by saggy sack October 26, 2010
That fucker is sniping a kill what an asshole
by Saggy sack March 29, 2016