Someone who when playing a dice game, does not role the dice all the way, and just smacks the dice down in the palm of his or her hand. Thus ruining the game. After one flapjacks it is socially unacceptable to ask for a do over.
"Yo mother fucker you flapjack more then an international house of pancakes."
"*dice roll* "Oh shit I flapjacked can I do over?"