My father convinced me that grawlixes (those "@#$%&*" symbols that sometimes appear in comics to represent swears) were pronounced "errr-rrr-rr-rrr-rrr-rrr-rr." Even though I'm an adult, I still can't stop pronouncing grawlixes like that.
A childhood belief about swearing

others believed things like this
- To this day my friend (he's 17) swears that chipmunks are baby squirrels.— Liz
- Until I was about four and a bit my father had me convinced that Friesian cows were called "big cats".— Chris
- My father convinced my little brother it was "Mount Reindeer" not Mount Rainier.— K
- I thought if 3 cards stopped at a 3-way stop sign then they had to stop forever until Christmas.Anon
- When I was young, I used to belive that
if you pushed the stop button in the bus it would stop for good.— Tom (Norway) - i used to believe that 'island' was pronounced 'is-land' instead. I know im not alone on that one! :)
— Da KornMeal