Due to a combination of factors, including loud musical instruments playing in the background (like in say, metal and punk songs), lead singer mumbling (i.e., Michael Stipe of REM, Bob Dylan), or just bizarre lyrics (here I'm thinking of folks like Beck), it's common for people not to be able to tell a song's lyrics. This is one of the most typical complaints against rock/popular music, although proponents fail to realize 1) If we like the song otherwise we don't care 2) If you listen enough you can learn most/all of the words 3) With the internet you can find out the exact lyrics within seconds.
There's a long history of this phenomenon. Apparently there was no crime in the 1960's, as the FBI had a reported 31 month long investigation into whether the words to The Kingsmen's cover of "Louie Louie" were obscene. Which is hilarious in retrospect, as the actual lyrics are incredibly simplistic and tame, even by the standards of the time. Granted, motivated people could easily come up with dirty versions of "Louie Louie," but that's hardly The Kingsmen's (or the song's writer Richard Berry's) fault. (Speaking of knowing, contrived dirty versions of pop songs, my classmates and I at middle school dances would sing the refrain from Quiet Riot's cover of "Cum on Feel the Noize" as "Girls FUCK your boys" instead of the actual "Girls rock your boys." Note: We were the only kids, anywhere, at anytime, to make this clever change.)
As entertaining as these willful changes are, I find the accidental, allegedly sincere mistakes somehow more funny. On that note I'll list a few examples.
1) AC/DC "You Shook Me All Night Long." Real lyrics--"She was a fast machine, she kept her motor clean." Misinterpreted--"She was a fax machine, she kept her modem clean."
2) Jimi Hendrix "Purple Haze." Real--"'Scuse me while I kiss the sky." Misinterpretation--"Scuse me while I kiss this guy."
3) Robert Palmer "Addicted to Love." Real--"Might as well face it, you're addicted to love." Misinterpretation--"Might as well face it, you're a dickhead in love."
4) Elton John "Tiny Dancer." Actual--"Hold me closer, tiny dancer." Misinterpretation--"Hold me closer, Tony Danza."
5) Alanis Morissette "You Outta Know." Real--"It's not fair to deny me, or the cross I bear that you gave to me." Misinterpretation--"It's not fair to deny me, or the cross-eyed bear that you gave to me."
6) The Go-Go's. "Our Lips Are Sealed." Two misinterpretations of the song title/refrain--"I love Cecile," and "Alex the Seal."
7) Billy Idol "Eyes Without a Face." My uncle thought the title/refrain was "How's About a Date?"
8) Manfred Mann's Earth Band's cover of Bruce Springsteen's "Blinded By the Light." Apparently an extremely common mistake. Instead of "Revved up a like a deuce," people hear "Wrapped up like a douche."
9) The Clash "Rock the Casbah." This is one of my own, perhaps indicating that I had a slightly dirty mind as a ten or eleven year old. I heard the title/refrain as "Fuck the cat's butt." Which I find makes a great song even more fun to sing. Try it.