I've always been afraid that Hannibal the Cannibal was in the sewers, and that he would eat your butt if you sat on the toilet too long. This is partly due to seeing The Silence of the Lambs and cartoons where alligators were in the sewers at a young age and getting them confused.
A childhood belief about fear of

others believed things like this
- I used to believe there really was alligators in the sewers— Makron
- I used to be scared that if I chewed my cuticles and swallowed a piece of skin, I would become a cannibal. Anon
- My little brother was afraid of toliets cuz he thought monkeys would jump out of his butt.— ~~~ Crazy Bro ~~~
- I used to believe that crocodiles lived in the toilet and would bite my butt when I had to go to the loo.— Oz
- i used to think that when i was pooping a crocodile could come out of the toilet and bite my butt off.— derek
- I didn't mind eating lambs brains when I was a kid because I thought it would make me smart.Anon