an American used to denote pompous, rich, stuffy, vainglorious, snobby aristocracy types who think they rule the world. Even if that is so, there are millions of planets orbiting millions of stars in this galaxy and in millions of galaxies, so the muckety-mucks can put that in their pipes and smoke it.
when I was eating at an Olive Garden in downtown Toronto, I asked this righteous babe of a waitress where the reputed Eaton mall was and what kind of people shop there. I had to define "muckety-mucks" to her since that term isn't used in Canada. I explained "fatcat", and had to define that word for her, too. She explained to me where I needed to go and remarked about my American vocabulary. We talked some more, then I payed the bill and laid down the tip and I was on my way.