I will add this as well:
First, keep in mind vaping is still new, and as someone pointed out, a counter culture meaning, many people don't understand it, and some don't even know what it is, police included. Now I can tell you in my particular department, many of us vape; however that does not transfer to every single police officer within the country, especially given again, this technology still being new and secondly, given that some devices are already produced for things other than nicotine.
Now for those in this thread who have taken time to educate those officers, I really do applaud you. I can tell you as an officer although our ...... as someone earlier so eloquently put it is to "serve and protect", my job also requires to be curious and watch for suspicious out of place behavior. Lets be honest, fogging up your car is typically synonymous with another type of behavior. Bear in mind that reasonable suspicion, not probable cause, which is a higher level of suspicion, is all that is needed for an officer to question you about such behavior. Realistically, if you explain to that officer what it is, and what it does, that will quell that curiosity. Now I cant't sit here and tell you that every officer is a good officer, I can tell you that about 99% of us are. I can tell you that most stories on the news that try and paint an officer as a thug and invincible are wrong and typically have other circumstances that are not revealed because it wouldn't make for good news.
My biggest pet peeve when I see threads like this pop up are this, first as an officer, I truly feel aliened from a community I enjoy because of the amount of ignorance that is displayed for my profession. Second, I have a hard time recommending fellow officers to this forum to help them when they are ready to quit analogs when I observe the amount of anti police sentiment stated in threads like these.
What bothers me most is many seem to be ok with alienating the e cig community from the police, when really, just like a normal citizen you should be helping educate because if you really believed in furthering the cause that would be your ultimate goal. I can tell you as someone who has worked in many realms of public service, firefighting, police, corrections, and EMS, there are alot of smokers. You would be surprised at the amount of those public service individuals who would actually welcome a conversation about vaping because they have tried everything to quit cigs as well.
To all those who would criticize my profession, I would challenge you this, go down to your local department, and go on a ride along, try it for a couple of shifts. Take a walk in my boots. You might be surprised at how much you do not know, or understand about police officers.