Why is it considered “taboo” to talk about your money, how much you spend, income etc…?

I was recently talking with this rich guy who owns a big business.

And I asked him about where he works, how much he gets paid, and he said very quickly “twelve hundred”. I didn’t get it at first, but he meant to say 1,200.

He was shy, and seemingly trying to keep it private, and said it fast like if someone heard it, then the whole world would know.

Another time, one of my friends was wearing $250 shoes, and I was talking to him about his shoes, he became uncomfortable when I brought up the price of it, and how they’re good quality. He quickly changed the subject about his work before needing to go.

Just most recently I was talking with a uni friend of mine, and he was wearing an almost $700 watch, I asked him about the price of it, and he gave me that look like where he was smiling and pissed at the same time, as if I asked an inappropriate question. He later then told me not to ask that again.

Why is it so bad to talk about money? It’s such a risky topic for some, but we deal with money everyday.