This will normally take the form of you being asked if you ever feel that maybe one day you will return to the truth.
My reponse would be, "I stopped considering it 'the truth' when I found out most of the things the society said about themselves were lies. I just can't be a part of an organization like that."
I still get occasional 'pass around the joke' emails from someone whose whole family we had been close to. If she ever asked I'd tell her the truth (gently), but since she doesn't ask I don't bring it up.
Another former friend who is an elder's wife who was also on the 'joke list' apparently saw my name among those being forwarded, and sent me one of those "are you approved assocation?" questions along with a "I hope you haven't fallen into false religion, come back to the hall" comment.
I told her that, when we were studying with JWs, we were told that, no matter how difficult it was, and no matter how much it upset our friends and family to become JWs, that you should not stay in a false religion just to please others.
I told her that, no matter how difficult it was to upset and disappoint our friends who were JWs, once we had found sufficient evidence that the society was not who it claimed to be, we could not in good conscience remain JWs just to please others.
They never know what to say to that, using their own arguments against them...