Oh, don't give me that look. That's my point. The fact that you've got things you don't want talked about means that others do as well, so it's not good to drag them through something that makes them uncomfortable unless they really have it coming. It's the Golden Rule.

Now that's trickier. It'll vary from person to person, so you just have to see what subjects make them uncomfortable... without actively prying for that, mind you... and go off from there.