I've been stopped a several times now while vaping in public. The best response I have found to use is goes something like this:
Offended person: ARE YOU SMOKING IN HERE?!?!?!
Calm me: "It's not a cigarette, it is a replacement, a fake one I am using to quit smoking." (takes cartomizer off) "see there is no tobacco and no fire, it's not real, it's just a vaporizer and it helped me quit smoking tobacco."
Response "Cool! Where can I get one for ______?" (me, my mother-in-law, my son, my Aunt Millie)
This seems to work much better than pretending to put my Vapor King out on my 11 year old's forehead. Gotta say, putting it out on my kid's forehead is fun, tho.