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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."
by Raul Chavez February 18, 2006
When a Bobby (anyone wearing an English police hat) throws someone down, handcuffs said person, pulls said persons pants to half mast, and proceeds to force a Billy club up said persons ass.
On the way to Kates birthday party, someone jumped me and gave me a dirty Bobby
by SmocknessMonster May 14, 2013