A moment during a film when a stupid, childish visual joke is inserted into a somewhat serious scene, removing the suspension of disbelief and tarnishing the scene (and sometimes the movie), rendering that segment almost unwatchable.
Origin: From the film "Raiders of the Lost Ark." During the truck chase scene, Indiana Jones and a Nazi are fighting for control of the truck carrying the Ark when the truck crashes through an irrigation system. The result is a very surprised Arab on the hood of the truck, staring at Indy and the Nazi from the wrong side of the windshield.
Dude, "The Dark Knight" was a great movie except for that "Arab on the windshield" moment in the tunnel when Batman simultaneously blows up one of the cars those two kids stuck in traffic were shooting with their fingers.