From what I've always understood, which is not much... It's those sentences mixed in many different ways "Hard, dont let it hit me, anytime" "Hard, dont let it anytime" "Hit me hard" "Du du du duuuu" Maybe it's none of this, but at least you can pretend it is and have fun singing along.
It's called vocal chops (I think). Basically you take different parts of a sentence, talking or singing, and you pitch each cut out vocal to different notes to create a melody
