I've always considered myself middle class. As a kid, I was probably in an upper middle class family, possibly even a wealthy family depending on your metrics. But we vacationed in a cheap area, didn't have cable, ate out once a month at most. I didn't play travel hockey, I played house league, Dad had 10 year old Mercedes and Mom had Hondas and Buick's and Toyota's that she kept for 10 years. The house was nice and big by the standards of the time, but nothing luxurious.
So were my parents frugal, cheap, miserly, or wealthy/upper middle class? We lived in a very nice area, but there were more expensive suburbs near there. Dad could have joined an expensive country club, but he funded our college educations instead. Other than the HCOL area, we lived like a lower-middle class family, but never had to worry about money... because we lived like that.
When I was out of college, I lived in a crappy apartment, I made $15 an hour, had a second job, drove a 20 year old car, and didn't have money to do crazy vacations or cable TV or a smart phone. But I did have money to save 35% of my salary to my 401k. Because of that, by some of the estimations above, I'm upper class today - because I was able to save what was a small dollar amount, but a large percentage of my salary from 22-25. Also because of that, I am well into positive net worth if you assume that my house is worth what I could sell it for. But right now I'm trying to figure out if we can afford to replace our AC unit so we can stop using window units. We can't, because the roof needs to be replaced soon and that is something we will HAVE to do. Gonna have to do another summer of window units.
Also not included in this is your family status. If I made $90k as a single person, that is pretty high up on that class system. $90k for a family of 4 in Chatanooga, TN? Baller. $90k for a family of 4 in Chicago? You're doing fine, but you're not doing great. And if that $90k is 2 parents working making $45k each, that doesn't go nearly as far as one parent making the $90k. I had more fun money when I was making $15 an hour than I do now, making quite a bit more than that.
What about your safety nets? Mine are my parents, even though I'm 31 and my wife is 32 and we're both currently employed and have a decent emergency fund. They're fine with that. It lets us build our wealth quicker, take more risks and not deplete the emergency fund - we pay my parents back when we can, which is usually pretty quickly. It means that we don't have to dig into the retirement accounts when E36 M3 hits the fan. So we have a huge leg up. I just used it to refinance our house last year. I sold my dad a guitar for $3,500, because I needed more liquidity and couldn't sell some stock because it wasn't vested yet. I bought the guitar back two months later.
You can't say someone is in any particular class by their income, or their net worth alone, or even combined. You have to look at the whole picture. And it is going to be viewed through a different lens by everyone.