When I was eleven or twelve, I saw the live-action Smurfs movie and there's a scene where a human says, "Stop saying, 'smurf' for everything! I mean, what does it even mean?! Smurf! Smurfitty smurf smurf smurf!" and a Smurf replies, "There's no call for that kind of language!", so I thought that "Smurfitty" was a swear word.
A childhood belief about swearing

others believed things like this
- I thought live-action films were very, very well-drawn cartoons.Anon
- i used to think the word "suck" was a swear wordAnon
- I used to believe that bizarre was a swear word.Anon
- I used to believe that “shut up” was a swear word.Anon
- i used to believe that if you said a swear word you would turn into the opposite sex the next day— jess
- My cousin used to think that "body" was a swear word.— Jordan