I thought that "ass" was just a rude word for one's body, rather than specifically meaning the posterior. I thought this because of how people say "Get your ass out of here" when they want someone to get out.
A childhood belief about swearing

others believed things like this
- when i first heard the name "blow job",i thought the meaning of that word was blowing a snot out of your nose.— myuka
- I used to believe that some first names were specifically for children and some were specifically for adults.— Marco
- I held my breath near cemeteries because I thought it would be rude to inhale spirits. Anon
- My cousin used to think that "body" was a swear word.— Jordan
- I used to get mad when people used the word "native" because I thought they were making fun of my name!— Nate
- In first grade, I thought that if I've never heard of a word before, then it wasn't a word.— Destiny