Well, with colleagues it becomes an ethical issue at work. People each have their own rights to privacy, and a lot of fights get started at work over who is getting paid more than who.
With other people in general, its a very touchy subject. I have found that people who have money come off like they are bragging. Other people have less money and they dont want you to feel sorry or have pity on them. And surprisingly. the amount of money you have can have a large impact on what others think about you, and some people just dont want to get into that kind of drama.
