Some of them simply think they are royalty and nobility and the rest of us are just serfs.
An economist would say that the upper class, whether European, British, or American, lives principally on inherited money. The upper middle class or bourgeoisie was historically defined as the people who were rich, maybe in some cases richer than the upper class, but they earned all or most of their money. This would include successful physicians, attorneys, and business people, those who might have inherited some money but had to work hard and acquire quite a bit of education in order to be successful. So most of the rich people who are visible to us tend to be members of the upper middle class. Most people are unaware that there is an upper class in this country because its members are very reticent and private, for the most part.
Of course, class is not really a question of how much money you have, but how you spend whatever you have, what your tastes, values, and aspirations are, how you live, and how you conduct yourself. Our Founding Fathers may have done away with a hereditary nobility but they couldn’t stamp out human ambition.