The mean of Fo Shizzle My Nizzle is For sure, my nigger. often used when a Gangster or some sort of black person (or in some rare cases a white person) says it to his friends to make him seem cool or "gangster"
Rick: you sup joe
Joe: nutt'n much you?
Rick: same.... Oh shit its billy i hate that fag...
Billy: Yo Fo shizzle my nizzle dog