In regards to questions outside that particular situation of two good friends talking, I think it's good practice to be mindful of what questions to ask people. I'm even wary of asking people I meet at the pub or at parties 'where do you work?'. There's been times in my life where there was no simple answer to it and again, some grief tied up in the answer. I have occasionally asked that of someone I just met at a party and then wanted to eat my words when the fumbled answer made it clear it was such a bad idea to ask it. Nowadays I try to wrap it up to make it easier to answer for those who aren't working for whatever reason.
I think questions asked in clueless innocence are less intrusive than those asked by people who seem to think they have a right to know and are oblivious to subtle 'I don't want to answer that' hints.