I used to believe that animal tails were the same as human penises. Not in determining gender, but in that I thought animals peed out of the tips of their tails. (So I guess I thought a human penis was a tail)
A childhood belief about rude bits

others believed things like this
- When i was little, i thought dogs poop from their tails.Anon
- I thought a Monkey was just a baby Gorilla and when they grew up their Tails fell off!— Brainhead
- That hot dogs were made from rat tails.Anon
- when i was little i used to think i was the only human and everyone else were robots trying to act human.— Spikey
- When I was little, I used to believe that wind was caused by whales flapping their tails way out in the ocean.— Nanohawk
- I used to believe that waves were made by whales who lined up in a row and flapped their tails.— Passionola