If you go the gym a lot, you've probably seen someone misuse a machine or do an exercise wrong. But it probably wasn't as funny as THIS dude. There's a video online of some guy doing sit-ups at the gym, except he never actually does one.
He just lies on the ground with his legs in the air and throws his head up and down really fast, but never actually lifts his back off the floor. And the funniest part is how FAST he does them. In his mind, he can bang out about 75 sit-ups in 20 seconds.
(Search for "How Not to Do Sit-Ups 101." WARNING: The guy filming uses the F-word.)