Sometimes your lyrics are just plain better, darnit. I've had more than a couple of story ideas result from misheard song lyrics (although usually not ones that are that funny).
My first one, a fairly common one, was "There's a bathroom on the right", which caused my Dad no end of glee.
I got my first laugh at someone else in high school from one of my friends singing loudly on the bus about "The Dukes of Hazzard are in the classroom".
When I got to meet Terri Nunn, I bit my tongue to avoid mentioning I'd thought for years she'd been singing about "swimming through a pile of cheese".
I'm not immune by far in adulthood, and I've just about killed J. with "Chicken on my head... CHICKEN ON MY HE-YEAD!" and "Pepperoni ANGRY PEPPERS mushrooms olives chives".
My oldest running one I only realized a year or two ago, when I found out Mr. Mister was actually not singing about a romantic, introspective sci-fi hero. "Carry a laser down the road that I must travel" indeed.
So... what are your favorite/most infamous mondegreens? And Manfred Mann's "revved up like a douche" doesn't count, because EVERYONE heard that one. ;)
EDIT: I was just reminded of one of my oldest, which I JUST NOW found out the real words to... I knew mine were wrong but I couldn't for the life of me figure out what the real ones were. Nirvana's "Smells Like Teen Spirit": "And this, for my gift of feeding bears."