When I was little, I said "Hachy-bachy" instead of hibachi (those little outdoor grills.) So everyone started calling them that, and we even called propane grills "Hachy bachy" as well. When I was about 22, my father sent me to Sears to price "Hachy bachys." The guy at Sears looked at me like I was complete moron, and I at last discovered that there was no such thing as a "Hachy Bachy."
A childhood belief about speaking

others believed things like this
- Until I was about four and a bit my father had me convinced that Friesian cows were called "big cats".— Chris
- When I first started learning to read I was convinced that vowels were called barnacles.— Andy Howell
- I used to think an evil spirit type thing called Wango lived in my dog. I was terrified of that dog.— Franklin
- If you stare into a mirror in almost complete darkness, the devil will appear instead of your reflection.Anon
- I used to think that the initials NYC stood for "nobody you're calling" Anon
- From the Carpenters hit I always sang "calling octopus of interplanetary craft" instead of "occupants".— Paul