We had a great game based on "The Hangover"! Our missing NPC, it turns out, was not on the roof of the tavern, and we didn't recognize the plot at first (we were prepared for a serious game originally), but about a third of the way in we realized the puzzle ahead of us. Our missing friend, it turned out, was desperately clinging to the top of a very tall steeple in another city which we had to sneak in to due to, ummm, events that the party hopes we can forget! Overall it was a crazy fun session, good for a one-off. And I think someone has a bugbear bride somewhere!
What movies have you ever played as D&D or other RPGs, especially if you didn't recognize the plot at first (if ever)?