When refering to rock hard tits that are protruding from a ladies brazier; when a woman jumps and her boobs arent affected by the reactionary effects of gravity.
dude did you see the cafeteria lady today? her knuckle tits were bustin the seams
(while watching a 70s porn) dammit man, they just dont make em like they used to, shes must have pure steel loaded into those mammoth cannons
person 1) have you felt those knuckle tits yet
person 2) boob job gone bad man
person 1) it got a little weird didnt it