We don't usually go see martial arts movies because of the plot, but there are a few that stretch credibility to its utmost limits. Cracked investigated these movies. Take, for example, Heart of the Dragon, one of two movies in this list about mentally-challenged martial arts experts.
...when we first meet Danny, he's goaded into ordering all kinds of food from an expensive restaurant for his friends, none of which he can pay for. He's embarrassed and wants to go home. This is a mentally challenged man who's been taken advantage of by people he thought he could trust. Tragic.
At least, it would be if the staff at the restaurant didn't respond by instantly kung fu-ing the ass of a clearly disabled man, complete with wacky sound effects--every punch to his stomach sounds like Moe beating up on Curly.