I have a great one, from the White Stripes' "Blue Orchid":
"You're going to blow up
But I guess that there's just no pleasing you"
I thought, yeah, Jack is a bit weird, but surely even he wouldn't think that anyone would actually enjoy being blown up...?
Then I realised it was "You're given a flower".
When I was much, much younger, I misheard Elvis' "Stick Like Glue" as "Stink like poo", no joke.
And the best one I've ever had is from the Stones' "Salt of the Earth". The real lyric is "Let's drink to the lowly of birth", and I heard, "Let's drink to the lonely pervert". It really does fit in with the rest of the lyrics; I didn't even think it sounded strange until I looked them up because I couldn't understand something later on in the song.