While I can appreciate the wry humor in the answers in that link, I do not think that most of them are remotely appropriate to use in an actual situation.
My goal would be to have as few people as possible actually know that I'm carrying in the first place. But if asked, I think that whatever answer I gave, it would be tailored to how much I knew about the person doing the asking. But whatever answer I gave, I would begin it with, "Would you like the short answer, or the long answer?" If they indicated the former, then I would answer with one of those handy, but non-insulting quips like, "because I can, and because when seconds count, the police are only minutes away." If they indicated the latter, or asked follow up questions, then I would give a more detailed explanation, outlining my rights and duties as a citizen, pointing out along the way that armed criminals don't give two figs for the politically correct or the lawful, and that your government prefers you disarmed because it makes you easier to manage as a commodity.
I think I would also encourage, during the discussion, a full exploration of what it means to be a gun owner, what the RKBA is, etc., etc., hoping to bring them around to my point of view. Here's why I would take the trouble: I have not always been a gun owner, nor have I always been a supporter of gun ownership.
I did not grow up around guns. I never fired a .22 LR until I was 18. I never fired a centerfire anything until I inherited my dead father's 1911-A1 at age 38, which he had kept as a WW2 souvenir. I have mentioned on other threads that I spent 6 years working in a major ER, and with the 2 lone exceptions, all I ever saw of guns were the results of their criminal misuse - hundreds of times over. The prevailing view in the medical community, and most particularly in the Emergency Medicine community, is that guns have no place in our society, and I was very much a part of that world.
When I inherited my dad's .45, I figured that, if I was going to have a gun in the house, I should know how to handle it safely. So I called up a couple of buddies of mine who were at the time both sergeants in the California NG, and I asked them to teach me how to properly handle and shoot this thing. They were more than glad to induct me into the ranks of gun owners by both teaching me the hows, AND the whys. They were patient and respectful. In the process, they converted me from being a guy who was scared of the gun he owned into a guy who has started amassing a collection, loves to shoot, is waiting for his CHL to come in the mail, and who is now an enthusiastic supporter of our 2nd Amendment rights.
Interestingly, the acquisition of this pistol also started me along the path of conversion from being a political liberal to being a political conservative - but that is another story.
The point of of all this is that my fear and loathing of firearms was based in literal ignorance. I was not stupid - just uninformed. If my friends had been dismissive or impatient with me, I might have remained that way, and to this day, I might have been voting to disarm YOU. Instead, they created a convert to the cause.
My goal would be to do that each and every time the issue comes up. Flippant and disrespectful answers will do nothing but alienate people who might otherwise be similarly converted. It helps if you start from the presumption that antis aren't stupid - they're just uninformed. At that point, it becomes our duty to inform them in way that brings them around to our understanding. If you deliberately insult them, then you drive them further into the anti camp; and at that point, you have become as much a threat to the RKBA as the antis.
Balance in all things.