I've turned a few movies off on my dvd before, and I've dozed off in theaters (mostly kid flicks) but the only time I remember walking out on a movie as a grownup was Iron Eagles III with Lou Gossett Jr. It was playing at the cheapie theater when I was so poor that was my sole form of weekly entertainment, and even at a buck it was the worst movie I ever paid for. Prophecy was another awful one (the mutant bear movie, not the one with bad guy angels and Christopher Walken in it).