1) the little sticky-out bone just above your asshole and below the small of your back. its where your tail would be if humans had tails, which would be kinda cool. it really hurts when u do sit ups cuz ur monkey bone gets pushed against the floor.
2) a film where a monkey turns into a guy
dude1: owww shit dude that fuckin canes, i cant do any more sit-ups
dude2: cansarn that infernal monkey bone, fucker.