There's a Beach Boys song that goes, "And she'll have fun, fun, fun, till her Daddy takes the T-Bird away." I always used to think he was singing, "And she'll have bun, bun, bun till her Daddy tells Mr Peters." and had this mental picture of a little girl stealing buns from Mr Peters the baker.
Another Beach Boys one -- for the song Help Me Rhonda, my brother used to sing "Help me Barnaby, help help me Barnaby.... help me, Ron, oh yeah -- get him outta my car." And it's supposed to be "Help me Rhonda, help help me Rhonda.... help me Rhonda, yeah, get her out of my heart."
The REM song, Losing My Religion. I could have sworn Mike was singing "Let's pee in the corner. Let's pee in the spotlight. Losing my religion." It's really "That's me in the corner. That's me in the spotlight."
My best buddy and I were in Pizza Hut singing We Hate It When Our Friends Become Successful by Morrissey. When we got to the end of the first verse my buddy sang, "Oh look at those clothes!! Now look at that place in SoHo!! Oh look at him now -- it's really laughable...." The real words are, "Oh look at those clothes!! Now look at that face, it's so old!! And such a video, well.... it's really laughable...." Also, the first time I heard that song, I could have sworn Morrissey was singing "Let's really laugh at them." instead of "It's really laughable."
I used to be in a drama group when I was small and at the beginning of every class we warmed up to Michael Jackson's Billie Jean. I could never, ever understand the words, so when my buddies used to sing it, I sang, "Billie Jean is, buh buh buh, she's just a girl who chins that I am the one, but the chin is not my son." or "Billie Jean is at my door....but the chair is not my son."
In the Smiths song A Rush And A Push And The Land Is Ours, I sang to a buddy of mine, "Your youth may be gone, but you're still a young man, so phone me, phone me.... so f**k me, f**k me, f**k me." and really it's just "phone me" five times.
A classic -- various mishearings of REM's The SideWinder Sleeps Tonight. First of all, I used to sing, "The sidewinder sleep, sleep, sleeps in the car." when it's "The sidewinder sleep, sleep, sleeps in a coil." And then there's one of the most famous misheard lyrics ever, second only to excuse me while I kiss this guy. These are all the variations I have heard of this one lyric.
I heard "Call me Cheryl Baker."
My other half heard "Calling Jamaica."
My father heard "Calling Chuck the baker."
A buddy of mine heard "Calling eachother a w**ker."
A different buddy heard "Calling Cheryl Baker up."
My brother heard, "Only in Jamaica, mon."
That's all.
A childhood belief about misheard lyrics

others believed things like this
- I used to think Buddy Rich was called Buddy Rich because he was my dad's friend, same with Buddy Holly. Anon
- When I first heard the song "Constant Craving" by KD Lang, I thought she was singing "God save gravy."Anon
- i thaught the michael jackson song billy jean song said Janet's not my son Anon
- When I first heard Matt Monro's song "Born Free," I thought he was singing "Porn Free."Anon
- My buddy used to think that when Steve Millers sang "Jungle Love" he was actually saying "Chug-a-lug" — Harold
- When I first heard Bruce Springsteen's song, "Born in the USA," I thought that the song was "Porn in the USA"Anon