So I was just watching Raiders of the Lost Ark, and it was on the scene that had Indie threatening to blow the Ark up with an RPG.
Slight problem with this though. This took place in 1936. The prop he was using was an RPG-2, which wasn't invented until 1949. Sure, Hollywood getting weapon props wrong, not that big a deal. The real issue was the fact that the RPG didn't even enter any military service until 1942 with the American Bazooka, followed shortly by the German Panzerfaust.
So what are some classic Hollywood blunders that you've caught?