I used to believe the line of the song "Wish I had an Angel" by Nightwish that went "Drunken disguise changes all the rules..." was "Drunk candy skies changes all the rules..." I thought the singer, the person who wrote it or the person it was about was on drugs.
I also thought the line of "Holiday" by Greenday that was "Just 'cause because we're outlaws yeah..." went "Just cause because we're out of gas..." I always laughed at that since it didn't make sense to me why they would pulverize the Eiffel towers because of that.
A childhood belief about misheard lyrics

others believed things like this
- I thought that Tommy Lee (the singer) and Tommy Lee Jones(the actor) were the same exact person.— Glowworm
- I used to belive that the law was a number of rules on a notice board outside Buckingham Palace.— Nathan Vasey
- I used to believe that anonymous was a person, and I thought, "Gee, this person writes a LOT of poems!"— Katie Albano
- i thought the line "saving my face" from the KT Tunstall song of the same name was "shaving my face"Anon
- I thought the line in the song "more than a woman" was "four-legged woman".— boo
- I thought the 'dubbing mixer' on TV credits was the person in charge of stirring the make up for the actors.— Clive