I had a really bad fit during one of the silent parts in the third starwars- film.. when Palpatine started to explain something to Anakin about the force. I just couldn't help it. "...it can bring back the deeead". Or "save your loved ones". It was almost as bad (the laughing fit, I mean) as when we finally got to know Bobbafett's reason for being so awesome - it wasn't that he never died, see, he just had so many clones to kill off. And I went "aha! So that's where all the Stormtrooper fodder comes from!".
Worst thing is the commercials, though. I don't watch TV, so I often see the commercials for the first time in the cinema. And no one laughs except for me, because everyone else have seen it a hundred times before..