What is Knucklin?
1.
A more aggressive version of
"Yo, bra, why's your hand in a cast?"
"I broke it knucklin' your mom last night."
-or-
"Why are you walking so messed up, were you riding a horse?"
"Naw man, I spent last night getting knuckled by 8 dudes and now my ass is broken like Angel's face from Fight Club."
See