When I was a kid, the song "I fought the Law" (I'm not sure who sang it) but I went years beliving it was "I fought the log, and the log one." I thought it was about a lumberjack.
A childhood belief about misheard lyrics

others believed things like this
- I thought Jedi fought with Life Savers... I never questioned it either! Anon
- Since he had fought in WWII, I naturally assumed my grandfather had killed Hitler himself.Anon
- I was very young during the first gulf war and I thought that it was fought in the gulf of mexico.— Kay
- i thought I got one year older when my family sang the birthday song.— I am the ghost
- for my little sis -
Paul McCarty song "Band on the Run" but when she sang it it was "Man has the Runs"Anon - I used to think that the actors on tv shows sang the show's theme song.Anon