My brother told me one time when I was about 4 that if I drank milk and threw up, it would come out in cubes.
I believed this until I was 13 and was amazed when it didn't work that way.
A childhood belief about milk

others believed things like this
- My Granny said if I drank milk and ate fish at the same time, I would die.Anon
- Chocolate, they say, rots your teeth. I believed if you drank chocolate milk, your bones would be brown.— Dellio
- I used to believe the milk would get sad if all I ever drank was koolaid.— al
- I used to think that if you drank too much milk and had a nosebleed, your blood would be white.— Tina
- i used to beleive when you drank milk your breasts would get bigger so i used to look down at them afterwordsAnon
- I thought black people were black because they drank chocolate milk. — Shelby