Kiss' song "I wanna rock and roll all night" - I thought it was "...and part of every day" (instead of "and party every day").
Also, Bruce Cockburn's song "If I had a rocket launcher" - I thought it was "if I had a rockin' lawn chair" (the next lyric is "some son of a b**ch would die" - odd!)
A childhood belief about misheard lyrics

others believed things like this
- I thought that the song "Built this City" by starship went as follows. "Milk and Cereal, Rock and Roll"Anon
- When I first heard Bruce Springsteen's song, "Born in the USA," I thought that the song was "Porn in the USA"Anon
- I use to think that Bruce Springsteen's song "growing up" was called "throwing up"— glowworm
- I used to think Bruce Springsteins song, "I'm the Nothin man", was "I'm the muffin man"....who knew?
— Toothfairy - I thought Rock and Roll were 2 musicians, with one who rocked and one who rolled.Anon
- I thought the song "Party Time" by Moby was actually saying "heart attack" (this was before I knew the title)— Elviessa