Given that you know you can talk to me about things in general, I'd think that this wouldn't be met with "It's none of your business" if it wasn't anyone that I knew - I'd think you'd try to use that angle immediately. If it's none of my business, however, I'll just assume for now that it's someone I know reasonably well. And if it's someone you're considering a friend, it's obviously someone you've known for at least a while...
1/3
[ohohoho, so we're going to make a game of it
excellent]
Given that you know you can talk to me about things in general, I'd think that this wouldn't be met with "It's none of your business" if it wasn't anyone that I knew - I'd think you'd try to use that angle immediately. If it's none of my business, however, I'll just assume for now that it's someone I know reasonably well. And if it's someone you're considering a friend, it's obviously someone you've known for at least a while...