I used to believe that every time you had sex your penis would get ywice as big.
A childhood belief about sex

others believed things like this
- I used to think that Frankie Avalon sang, "Hey Penis, Oh, penis..." instead of "Hey Venus."Anon
- I used to believe that a boy's penis came out of his bellybutton, so you couldn't see it all the time.Anon
- I used to believe that gay sex involved a man sticking his penis inside another man's penis.Anon
- I used to believe that gay guys had sex by sticking their penis in the other's penis.— Fanbrat
- I used to think that men's poo came out of their penis' like wee.— Helen
- I used to think that I was the only person to have a penis!Anon