I had the same problem with "Single Ladies" by Beyonce. Instead of "Ladies" I heard "Legs" So it was a song about people losing a leg because they got careless and didn't show appreciation. So now they are on the look out for new ones.
I'm still disappointed about when I found out that one Soul Coughing song wasn't about con men: "You get the angles, and I'll get the rest", but the lyrics were actually "you get the ankles, and I'll get the wrists"
Not long ago i heard the Theme from one of my favourite Animes as a child and it was just one word I sung wrong but theat one word ruined the song for somehow.
I have a really hard time understanding the lyrics when I listen to songs (maybe because I'm autistic and have some auditory processing issues) so I'm often wildly wrong about them.