At the risk of sounding Marxist, there's only really two classes. If you have to trade your time and labour for money, you're working class. If your money makes money and you can live off that, you're capitalist class.

We stratify working class into different sub groups (blue collar, white collar, professional, middle class, working poor, etc) to develop a sense of hierarchy, and it really rubs people the wrong way to be told that they're no better (or worse!) than the guy sweeping the floors.