I used to believe "fuck" was an even worse word for "penis" (I was around 7, "penis" wasn't said louder than a whisper, if at all).
A childhood belief about swearing

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 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
- i believed that penis's were hotdogs— Justin (Visualizer)