I was also quite afraid the first time I saw an erect penis, because I didn't understand how it would fit. They kind of left that part out of sex ed.
A childhood belief about rude bits

others believed things like this
- I used to believe that when a boy was curcumcised they cut off one penis, which is why I only had one left.— whoops!
- I thought a Prime Minister was some kind of religious leader, due to the "Minister" part— Darth Carrietta
- I used to think that boys didn't get their penis until they were 18 which was legal adulthood! — beckles
- I used to believe that every time you had sex your penis would get ywice as big.Anon
- I used to think that Frankie Avalon sang, "Hey Penis, Oh, penis..." instead of "Hey Venus."Anon
- I used to believe that a boy's penis came out of his bellybutton, so you couldn't see it all the time.Anon