You know you've done it. You're listening to a song, you have no idea what's being sung, but later as you sing it to yourself you realize you've supplied some creative lyrics. Classic example? "Blinded By the Light," which, if you believed everyone who sang it, includes the line "Wrapped up like a douche." Here's a heavy metal example. I've never heard of Children of Bodom, but a couple fans have, and this is what they came up with.
(Thanks, Say No To Crack, and Team Twelve's Steve-O Five and Mike Seven, whoever you are!)