This is when you get some beefcake who thinks hes hot shit to show off. Tell him that you are going to put a towel over his head and see if he can do the situp while you pull down. Being the arrogant moron that he is, he gladly tries. Have someone pull their pants down over his head and release the towel. The unsuspecting douchebag's nose goes right up the guys ass.
I wish someone would give Arnold the power situp.