There exists a lot of literature about class, which is a very fluid term. I think to the extent that people react really negatively when you suggest $100k is upper class, they're reacting to other associations they have with that term. For example, educational attainment or social advantage are also class markers, and many people at $100k won't particularly have them. For another, material advantages of being wealthy are, at many locales, absolutely unobtainable at only $100k a year. House ownership is a major one. International travel is another one that is high on the SWPL list, which many people who are doing well for themselves at $100k a year will not find themselves able to consume. (Chiefly, because in return for that $100k they've committed themselves to a career track which doesn't tolerate 2 week vacations very well.)

FWIW, there's a lot of talk in the United States since about 1970 or so of there being a "professional class", which has education and income markedly higher than the traditional middle class but which has lifestyles which resemble middle class more than the traditional upper classes. It was traditionally filled full of doctors, lawyers, and accountants. Engineers are entering the professional class, which discomfits a lot of people.

A class is not about what you can buy, or what people think of you. It is about SOURCE of your income, not where it ends up.

The concept of class was invented by Karl Marx, a person belongs to some class based on his/her relation to the means of production. There are 3 factors of production: labor, capital, and land (that final one is of much less importance now than it used to be in Marx's era, but still). So there are classes: middle class are those deriving their income from work (rent on their labor), rich deriving their income from capital, and aristocrates deriving their income from land (these are now extinct). Poor are those who don't have any means of production, so they depend on social transfers like foodstamps. Of course these sources can mix in a single person - like a coder who rents out spare bedroom on airbnb, or a top manager who has some stock of the company he runs in addition to salary and bonuses, and gets some dividends on it - but the largest one 'wins'.

Because the IRS collects sources of income of people (because they are differently taxed), and publishes summary of its results, it is possible to make a very precise picture of American class structure/thresholds of classes. It is just that nobody likes these results.

It was 350K in 2009, in the midst of a crisis (incomes of people like that have a lot to do with performance-based bonuses, stock appreciation and the like, so they dipped a lot in the crisis, much more than oridinary people's). In 2012 it was already $560K.

And the definition for upper class as being top 1% is arbitrary, it is in fact invented by Obama during his first presidential campaign, solely for finger-pointing (he could safely say 1% is not many people so they won't impact election results enough and safe to be finger-pointed).

Upper class are ought to be people who don't derive their income from work, but from their property - business profits, stock dividends, rent etc. - in all societies upper class are those who DON'T depend on salary, and many of them don't work at all. So it is natural to define upper class income threshold as a point above which less than 50% of income comes from employment. In the present United States, this is about 3-4 million bucks a year per household. This will be economically defined upper class, not just some 'people rich enough to hate them'. So McCain was closer to reality back in 2008 is his upper class definition.

I personally don't know anyone making that much, but i can safely say that all people i know making 150-1000k a year will be broke months or at most, a year or two if they stop working, with one exception (a guy living in East Asia with about 400k of annual income, who never married or had kids). So they are not upper class. And i am speaking of the places which are cheaper and have lower living standards than USA.