My boyfriend's 18 and he thought that periods only last one day! I told him and he was very surprised and said that he's really glad he isn't a girl! :)
A childhood belief about periods

others believed things like this
- My mom told me sex was people making out with no clothes on, boy was I surprised in middle school!— Amie
- I also used to think that Mommies didn't have periods. I thought it went away once you had a baby.— T
- i thought the phrase "getting a boner" referred to men getting their periods. — astrid
- When my mom was a child, she thought that while girls had periods, boys had hemorrhoids!Anon
- I thought that days had 100 hours in them. Very surprised to hear there were only 24.— Cassiopeia
- When I first met my husband, he thought women didn't fart. He was really surprised after he met me!!!Anon