Mettaton is an evil warlord.

Megatron is the popstar of the Underground.

Mettaton is also macaroni.

Which makes me think of the feather in the hat of Yankee Doodle.

So that makes Mettatron the evil popstar of Cybertron but he is also a thing of Macaroni, which is also a feather in the hat of Yankee Doodle. Ayyyy, Macarena!