Without spoiling too much, if you've ever seen Toy Story 3, you'll remember that the movie almost ends on an extremely bleak note. As a prank, YouTube user Justin Wallin recut the film with this extraordinarily traumatizing ending and screened the entire film for his none-the-wiser mother. This video runs a little long, but the deliciously evil payoff is within the first three minutes. [Justin Wallin via MeFi]
That's one of the most evil pranks I've ever seen. Well, aside from the fact that Pixar put in that whole sequence so bleak. I thought they were actually going to end like it too.
*bonus: Pet peeve #4209209: Calling a Pixar film a Disney film. No one calls the Avengers a Disney film, why Toy Story?