No wonder they can’t shoot straight (Star Wars – A New Hope)
This could be one of the most famous additional mess-ups of all time, so much so that the film was edited retrospectively to fit it. So a group of stormtroopers chase down C-3PO and R2-D2 on the Death Star. As they enter the room where the droids are, one of the soldiers knocks his head on the bottom of the blast door. Twenty-seven years later, when George Lucas remastered the films for a special edition release, he included a comical “bonk” sound effect to accompany the blow. It’s almost as funny as Jar Jar! Almost.

No Wonder They Can’t Shoot Straight (Star Wars – A New Hope)
Ghostbusters, alright! (Ghostbusters)
Just before entering Dana’s Central Park West apartment complex for their final battle against Gozer, the Ghostbusters take in the cheers of New Yorkers who had gathered to support them. One extremely apparent red-headed extra continues to shout, pump his fist, and overall act as if this is the pinnacle of his life up to that moment, providing perhaps excessive support. Recently, an online sleuth discovered his identity: he was played by Eldo Ray Estes, a makeup artist who went on to win four Emmy Awards for his work on As the World Turns.

Ghostbusters, Alright! (Ghostbusters)