I used to think that men had pubic hair only after they had sex (don't ask why).
so one day when I was changing with a friend in a changing room to go swimming I saw he had a bit hair "down there". I was really shocked and asked him about it (he had a girlfriend). He, being a joker, told me with a straight face that he meant to tell me and yes, it was true, but not to tell anyone. I believed him! This held up for one uncomfortable week until he couldn't bear it any longer and told me the truth. I was so embarassed! (I was 12!)
A childhood belief about rude bits

others believed things like this
- I used to think pubic hair was really called 'public hair' until I was about 15— Spe
- I used to think that bleaching your hair meant washing your hair with toilet bleach.Anon
- I believed that if you ate a piece of your own hair, a new strand of hair would grow on your head.— Ryo
- I used to think that everybody's hair was black and if you had blond hair, you dyed your hair.— ~_~CoolKid93_~_
- I once told a friend of mine that if you held in a smelly burp, it'd turn into a fart. She believed me.Anon
- I used to believe that the sun was an oversized colour changing M&M.Anon