As a kid, my buddies and I used to change the lyrics to songs and make them dirty. We would make them as nasty as possible - which means a lot of "poo" references, considering we were 8, and didn't know about much else.
Some people are scared of monsters, some are scared of midgets. These people will be having "Frosty The Snowman" nightmares for the rest of their lives...
On a side note, in case you were thinking about attempting something like this yourself, watch the second video to see what happens when the prank goes wrong