I met a male Protestant for the first time and I found it odd - I didn't think there were any male Protestants. As a child I had always thought that Protestants were the people who roam the sidewalks at night asking sex for money.
It was only after that I found out those were actually "prostitutes".
A childhood belief about church

others believed things like this
- I thought the word mailman was male man and it seemed dumb to me as aren't all men male?— andalite
- I used to think that to desex an animal meant to turn it from a male to a female or female to male.— Phil
- I used to believe, as a child, that horses were male cows.— Martin Taylor
- For the longest time I used to believe that the male ballet dancers were naked from the waist down.Anon
- I thought all poodles were female...i mean how can you be a male poodle and live with yourself?Anon
- We had a male cat that wasn't neutered. I thought his testicles were just the cat version of a butt.— Robyn