I used to believe that during an erection, a man's penis remained pointed downward. I couldn't imagine how a couple could possibly have sex in any position other than the obvious! Then my 9th grade health class showed (much to my shock!) a thermoscopic video of a man getting an erection. I think I almost said, "Ohh! I get it!" outloud (I didn't though!)
A childhood belief about rude bits

others believed things like this
- when I was little, about 4th grade, I thought that when a guy had an erection his penis turned colors...lmao— peanut
- i used believe and erection was when your testicles went into your penisAnon
- i used to belive when i got an erection that if i bent my penis it would break like a bone— beep41
- I used to believe whenever I got an erection it meant I had to pee.— Adam
- I used to believe that a homosexual is a man who doesn't have erection. — paatrik
- I used to believe that an erection was called a 'wallet'.Anon