Imho middle class means you work for a living, upper class means you can live on wealth.
You might also be surprised to learn that a $166,000/year household income puts you in the top 5% of US households. Definitely upper middle class but still pretty easy to burn your whole paycheck every month.
I always viewed the working class a subset of the middle class, defined by the fact that they did some sort of physical labor for pay. I.e. as opposed to office work.
