When I asked my mom what a vagina was (which I pronounced "bagina" for some reason), she didn't really want to tell me so she said it was "a woman's butt". Not only did I believe her, but I thought it must not be any more offensive a word than "butt" which almost got me into trouble a few times (almost).
I also thought that women didn't have pubic hair and that they peed from the vagina, which I also thought was why they couldn't do it standing up...because it would be too wide a stream to aim it into the toilet.
A childhood belief about rude bits

others believed things like this
- i used to believe that women peed out of their arse and pooed out of their vagina— TIM wilson
- when i was 6 i thought girls peed out of there butt hole!— axel
- I used to think girls peed from their butt.— Neil
- I used to beileve girls peed out their butt 😂Anon
- I used to think that the b-word was buttAnon
- I use to believe that the man peed in the woman to get her pregnant. Didn't know about sperm until sex ed. — das