This isn't mine (seriously!) but I knew a guy who, when he was about 12, still thought the word "fuck" just meant the same thing as "shit", as I discovered when he told me a bird had fucked on his coat.
A childhood belief about swearing

others believed things like this
- My sister used to think that "spit" was a bad word. She meant "shit".— "Spit!"
- I thought it was "fuck-an-egg" until I was 16.Anon
- When I was thirteen, I thought that FTW stood for Fuck The World.Anon
- I used to believe that "nuptial" was a naughty word. I thought it meant nipple. XD— Sara Hagen
- For years I heard the word "pedophile" and thought it meant a pedicurist's tool.— Lauren
- I used to believe jaywalking meant walking around naked in public (from naked as a JAY bird...)— Izzi