Bottom line, these people are boors. See:
http://www.able2know.com/forums/viewtopic.php?p=653721#653721
Anyway, hmm, the question is if you want to burn the bridge or not. I've burned a bridge or two on that, but since I don't practice law any more (and pretty much despised doing so when I did), it didn't matter much. I used to also pull the ethics card with my own family, "Well, since there's a possibility that I could have a conflict of interest in your affairs, because of our close relationship, I have to decline answering your question." If they persisted, I'd add, "Well, it would be an ethical violation and I could lose my license to practice law." And if they continued to insist that it was no big deal, I'd add something like, "My license to practice is very important to me. I worked hard to get it and it was not cheap. I would not like to lose it on an off the cuff question." And perhaps guilt would finally win out (by the way, unless it was my own mother, chances were good that it was not an ethical violation of any sort -- who, normally, inherits from their third cousin? -- but it was a convenient excuse and it often deftly turned the conversation to the direction of lawyer ethics and the like).
If you want to remain friends or keep the client, hmm, let's see.
For a client, it's probably easier. You can maybe push it off into the next time you see them, e. g. "Could you gather your questions all together, and then we'll discuss them the next time you come in? That way, I can devote my full attention to your concerns." If the client is persistent, you could probably add something like you work best in your office where you have access to reference materials (I can't recall what you do for a living or if this would be at all applicable).
As for a "friend", and I use the term loosely because I find such behavior to be so vile that I don't consider such people (who are, essentially, trying to take the food off your table) to be friends, maybe you can also go with the office environment/reference materials angle. Or set up an appointment. Or hand out a business card, e. g. "Let's talk about this during business hours. Right now, let's have some fun. How's little Ichabod?" and change the subject
fast.