When a female (usually heavy set) is receiving sex from a dirty juggalo kid who never bathes, WHILE on her period, the dick is pulled out and the male is sucked off to form a lovely mixture of semen and blood. Also called the Dirty Lisa.
"Damn that fat bitch is prime for a Dirty Bobby!"
"Damn... you Dirty Bobby!"
"I'd like to have a Dirty Bobby Cocktail."