A few favorites from ifyouwatchitbackwards.com:
If you watch Jersey Shore backwards, you see the entire United States become smarter.
If you watch Santa Claus backwards, you see a festively dressed, obese, thief of the night, with abnormal abilities to steal peoples Christmas presents at astronomical speeds. Going nation to nation via reindeer.
If you watch Mulan backwards, it’s the story about a great war hero who goes back home and gets a sex change.
If you watch Titanic backwards, it’s about underwater people repairing a ship with an iceberg so that they can sail to England.
If you watch The Biggest Loser backwards, it’s a bunch of people losing endurance and racing to gain weight.
If you watch Michael Jackson backwards, it’s a miracle story of a rich white pedophile who magically transforms into a sane black man.
If you watch 300 backwards, King Leonidas helps the messenger out of the well with his foot and tells him "SPARTA IS THIS!"
If you watch the 2008 Olympics backwards, it's really about Michael Phelps giving a bunch of medals to Chinese people. What a philanthropist.