'Star Wars: A New Hope' (1977)
While chasing down Luke, Leia, and Han Solo in the first Star Wars movie, a group of Stormtroopers bust a door open by shooting it. The only problem is, the door doesn't open all the way, and one of the Stormtroopers bumps his head while walking through. The accident didn't go unnoticed by director George Lucas who added a "boink" noise to make the mistake seem like it was intentional.