Why do people tend to hate all rich people whether they are good people or not?

My mom has a friend who absolutely despises the rich. She claims it’s because she wasn’t that well off growing up. My mom grew up very wealthy. Because of this, my mom’s friend attacks my mom anytime my mom says something about her childhood. My mom doesn’t flaunt her family’s wealth. She doesn’t brag or try to make it known how much money they have. Anytime she mentions something from her childhood, however, this friend makes a nasty comment. Recently, my mom was out with this woman and another friend and they were talking about jobs they held when they were younger. When my mom spoke up, this friend attacked her because my mom never needed to work when she was younger.

My question is this: Why are the rich often despised? My mom is a nice person but there are some people who hate when she makes any reference to having money. As she grew up wealthy, any reference to her childhood is a reference to her having money.