What song's lyrics did you get wrong?
One that comes to my mind--since I just heard it on a commercial-- is from a song (that I absolutely can't stand) by Hot Chocolate's "You Sexy Thing". When I first heard this as a child, I though it was, "I believe in milk holes, praise the lord, you sexy thing."
Also - It's "
Where you from, you sexy thing."

I did this all the time; sometimes deliberately:
Collective Souls December - "Turn your head" became "Taco head". Sing it once and you will Never Go Back.
Tori Amos' Crucify - "My hearts been in chains" became "my hearts been in cheeeeeeeeeeeeeeeeeeeese, wo oh oh"
Trad. This Little Light of Mine - "Hide it under a bushel? no!" became "Hide it under a bush? HELL NO!"
The Stranglers "Golden Brown" - "with my mind she run" became "with my manchurian" (By the way this is one of the greatest songs of the 80s)
And in the massive subcategory of misheard REM lyrics we have:
"Radio Free Europe" became "Greedier & Greedier"
"Harborcoat" became "Who is trying my Harder coat"
"Night Swimming" apparently "deserves a quiet life".
"Begin the Begin" had the weirdest lyric "invaginate me...."
"Its the end of the world as we know it" - Verbal Rorschach test except for the "Leonard Bernstein" part.
"Pilgramage" - We got "Called the bluff of the two headed cow" After many hours of argument, turns out............. that was exactly right.