A knuckles is a person who is a bad ass often using the catch phrase H.X.C (Hardcore) or often saying: Yo Yo Yo B Boy That Shits for Real Mutha Fucka’, for Shit, Bitch…Fuckin’ Ass and Blab Blab. Knuckles is also a sexual move where you shove your whole fist into a women's ass and say one or both of the two aforementioned catch phrases.
Johnny is a real Knuckles! or Yo dogg I gave my girlfriend
a knuckles lastnight.