I think this is part of that Japanese thing where they comment on how songs in other languages sound dirty/silly in Japanese? There used to be a clip on here where some Japanese dudes did a video for Come On Eileen that was all about sniffing doll panties or the like.
This one, I guess "Y M C A" sounds like "Jesus fucking shit there's a giant worm on my face."
I'm thinking they're some variation of those caterpillars that will sometimes hang at the bottom of a length of their own silk, just waiting to have some poor idiot blunder into them. I see a couple hanging in the breeze every year, and have occasionally walked into one myself.
Maybe they get them really bad in Japan? Like some kind of seasonal thing?
All I know is that the song at the very beginning is the same song our Japanese teacher used to make us sing all the damn day. And then it turns into manly screaming about giant threadworms? That's a transition I don't get.