Knuckle-Stuff Share definition Flag The action of inserting a closed fist into the vaginal or anal region. (more commonly known as fisting ) "Yo dog I just knuckle-stuffed my bitch last night." Knuckle-Stuff by coolguy7583 December 16, 2018 0 0 Get merch Get the Knuckle-Stuff mug. Buy Now — $32.95 See more merch