I thought I had invented the word "asshole". At this point I was too young to have heard it on TV. A few years later I was allowed to watch some films and TV with swearing in and when the word "asshole" was used, I was delighted. I assumed that in the few years since I had invented it, its use had become more widespread to the point that it had entered the English language. Go me!
A childhood belief about swearing

others believed things like this
- I used to believe that I actually invented the word "excellent".— poop jacket
- Up until 8th grade or so, I was convinced that I invented the word "Fart"— Jonah
- I thought that some animals had just been "invented" recently (like within the last 50 years or so)— Makron
- For years I heard the word "pedophile" and thought it meant a pedicurist's tool.— Lauren
- I used to believe my nieghboor jose invented the language spanish and he got rich and bought cars— Thomas
- In first grade, I thought that if I've never heard of a word before, then it wasn't a word.— Destiny