Momentarily disregarding the Tiny Toons video, I must ask a question and then try to answer it myself.

Who wins?

Because... Well, technically, Universe Man could kick the ass of anyone he wanted. But he's "usually kind to smaller man", which includes everyone, since he's the size of the entire Universe. So I think he's abstaining. He's not actually fighting. So he shouldn't even be in the song, technically.

And since Triangle Man kicks the collective ass of Particle Man and Person Man, then I suppose he wins the fight.

But only because Universe Man lets him!