Jwb, you are correct, it is rude. Even if a close personal friend asks me how I'm doing, I don't tell them, well I'm making X amount of money this year. It's just not a thing that I want to discuss. I'm doing fine. Isn't that enough?
Like you said, I don't mind telling people my back ground and what I do. But I'll be damned if I'm going to lay out a full business plan for them to follow. The road to being self employeed is not an easy one. Why should I hand over all my hard work and research?
Amy, it might depend on where you live. If you are living in a beach town and running some sort of tourist business, then the locals can see with their eyes what you do. I live in Santiago. My work is done over the phone and computer. There is no store, no bar, no hotel, no products, nothing for anyone to take a look at. It seems people will stop at nothing to find out how I make a living. I have even had my neighbors ask my kids. Rude indeed.
Jwb, is also right people wanting to know your net worth. Again, none of their business. I would never think of asking anyone that.