Over the last two years, I have been in many situations where I was dubious about whether to vape or not. In most cases, I play it by ear, try to be courteous to others, yet informative when given the opportunity.
One surprising episode involved my husband and I attending a big annual Cancer Society fund raiser here. I was concerned that in that environment, even vaping would be unacceptable. Alas, was I ever wrong. The event is held in an outdoor setting in the summer, but with air conditioned tents for auctions and the casino tent. I had stepped outside to vape a little and ran into a client of mine, an oncologist (transcription service). He was so intrigued and ask me to demo to his other staff who were there. Suddenly I found myself in the ambassador mode. Very good feedback and they encouraged me to vape at the card tables, in the tents, anywhere... which led to more demos but I was happy to do it in that situation, "for the cause" so to speak.
Other situations that have been interesting are outside the hospital, in the airport and various other public places. I don't force the issue, but I do expose others to the information and usually, done in the right way, it's a good thing.
Of course, I must add that here in the south, we are fairly gregarious in public and approaching total strangers is not an unusual thing here. I have even stood outside with smokers before going in a store, and introduced them to vaping.
I avoid the e-cig terminology as much as possible, using vaping and Personal Vaporizer when explaining, therefore avoiding the inate negativity the word "cigarette" inspires.
We are all adults (hopefully) and most if not all of us have a pretty good instinct about our immediate enviroment and how accepting others will be.
Vape on Vapers ! And keep those cards handy at all times !