I have to go with Tom Cruise. Besides the whole scientology and jumping on sofas thing, watch the behind the scenes for Mission Impossible 2.
Tom: "We need to make this fight scene more exciting. How about we have him stab a dagger TOWARD MY EYE?"
John Woo: "Uh...we don't have a special effect planned for that..."
Tom: "Eh, just wire it to a pole."
The guy is nuts. Still love most of his movies, though.