I had a friend in college who believed that testicles were internal. She has 2 brothers and didn't know they hung outside the body until we told her. She was in her Junior year at the time.
A childhood belief about rude bits

others believed things like this
- My brothers friend still thinks he will be a kangaroo when he grows up and he's 9!!!!!— Jane Rom
- The very first time I saw a globe (of Earth, yes) I asked where "College" was located.— Shade
- My dad told me that kiwi fruits were kiwi birds testicles. They are the right shape and kind of furry— jefnier
- a friend of my little sister's had 4 older brothers, so she thought that when you got older you grew a penis!Anon
- when i was young i believed Micheal Jackson and 'the artist formerly known as prince' were twin brothers.— tim
- I used to think that you have to have the same birthday as your parent to have "junior" in your name.Anon