I thought that the word "ejaculate" meant to laugh hard/think something was really funny. So when my former stepmom, dad, and step siblings were with me when I was about 9, someone said some kind of joke, and I cracked up and yelled "I'm ejaculating!" quite loudly. I got a few very odd looks. I'm still embarrassed to think about it.
A childhood belief about rude bits

others believed things like this
- i used to think the word "friendship" meant a special kind of rocketship that you went on with your friends.— chips ahoy!
- I thought the expression "so funny I forgot to laugh" was literal instead of sarcastic— Not so funny after all
- I used to think "premature ejaculation" was a boy ejaculating before he hit puberty.Anon
- I used to believe that "nuptial" was a naughty word. I thought it meant nipple. XD— Sara Hagen
- For years I heard the word "pedophile" and thought it meant a pedicurist's tool.— Lauren
- i used to think that when i got a hard-on it meant i had to pee.— mw