This isn't me but when my friend's brother was younger he used to call the 46A, (which is a type of bus) the fuckty-nix A, and a light, a shite.
Once when I was little I was sitting in the car saying nonsense words are getting my brother to repeat them. Completly by mistake I came out with 'cunt'. He wouldn't repeat it. :'(
Oh, and just the other day (I am 13) I called someone a prick in front of my parents. Not realising it was a curse. They set me straight. Well...after staring at me for a few minutes.
Last one, my friend (dunno what the story is but she doesn't really know about growing up and babies and the like) and me were talking. For some odd reason the word orgasm came into the conversation, so she shouts 'Oh orgasm' loudly not realising what it meant. I don't think anyone heard her though.
A childhood belief about swearing

others believed things like this
- I used to think an orgasm was a special type of orange juice because it sounded similar.— HaPpY
- I spent ages wondering what a bart ender was as a child without realising that it was actually bar tender.— Heather
- When I was younger, I think i can change my brother with a friend— Mbaclé du 55
- i used to think when you had an orgasm you were giving birth— splooger
- I always thought only boys could orgasm. — kg
- I used to think you had to get special permission from your parents to use curse words— zeitgeist