While filming The Wizard of Oz, Judy Garland was slapped by her director for failing to complete a scene.
During the scene in which Dorothy slaps the Cowardly Lion, Garland got a case of the giggles and could not stop laughing. Unable to get his lead actress to focus, director Victor Fleming brought her off the set and slapped her across the face! After returning, Garland was able to successfully complete the scene in just one take. (More weird Wizard of Oz trivia)
He later felt terrible and apologized for it. Years later, Judy Garland said that she still admired him as a director. Learn more about Victor Fleming in this video.