My parents would refer to bowel movements as B.M.s. I don't think I figured out that it was an abbreviation until I was in high school (I guessed that it was a word spelled sort of like "be-em," but could get no straight answer regarding this). Sometime later, one of my younger brothers used the term "B.M." around some friends at college, who had never heard the expression before in their lives! They were delighted with this new ersatz "bad word," and took to using it in creative ways. "Anyone in the bathroom?" "I am! I'm B-ing M!"
A childhood belief about swearing

others believed things like this
- In first grade, I thought that if I've never heard of a word before, then it wasn't a word.— Destiny
- I used to believe the word shoes was spelled shouse. It looked right to me... — Shouse
- I used to believe that you got married right after you finished high school or college. Anon
- I thought that wars had to last four years... just like high school and college.— A. Falk
- i used to think that the word "stupid" was a curse word, ranging in scale right beside the "f" word.Anon
- I used to think that fart was a bad word and then i heard my mom say it once and I was so shocked.— Tara