I had a similar experience with a campus cop at the university I work at.
I was sitting in my car in the faculty parking lot getting some materials together to take into my office. I was puffing away on my Volt Spinner the whole time. I noticed out of the corner of my eye there was a campus cop nearby, but I didn't pay him much mind. Next thing I know he pulls up beside me and gets out of his car. First let me say that this was a new guy to the campus police that I hadn't met yet. Secondly, I have a rather off-beat sense of humor and if I get the chance to mess with somebody, all in good fun and not to be mean, I will. So here I am getting stuff out of my car and putting in on the trunk and puffing on my Spinner and out comes the cop. He walks over to me and says:
"Good afternoon sir. I'm officer "new guy"."
"Good afternoon, I'm Dr.J. Nice to meet you"
"Uh sir, I've been watching you for a little while now and noticed you've been smoking something out of that device you are holding."
"I'm not smoking anything officer "new guy".
His brow furrows "I've been watching you smoke for the past few minutes sir."
"I'm not smoking"
He places his hands on his hips "Well if you aren't smoking, then why is smoke coming out of your mouth when you use that device?"
"It's not smoke"
Now he starts tapping his foot rapidly and seem rather agitated. "Well if it's not smoke than what is it Dr.J?"
"It's vapor"
A confused look on his face. "Vapor?"
"Yes, vapor".
"I don't understand what you mean by vapor"
"Vapor is produced by heat coming into contact with a liquid that..."
He interrupts me and blurts "I know how vapor is produced Dr.J"
"Oh, I'm sorry. I thought you didn't by your remark."
"OK Dr.J, let me put this more bluntly then sir. What is that you are smoking or producing vapor from and what's in it?"
"Oh this? It's called a Volt Spinner and it has a mixture of Propylene Glycol and Vegetable Glycerin in it with flavoring."
Around this time another campus cop pulls up that I know and he knows what my ecig is and gets out of his car to ask officer "new guy" what's up.
Officer new guy tells him that I'm giving him a hard time about him questioning me about my smoking device.
The other officer gets a slight grin on his face and says "That's not smoke."
Now officer "new guy" is getting really frustrated and about that time, me and the other officer start cracking up laughing. Officer "new guy" is clearly upset by this and raises his voice "OK, WHAT'S GOING ON HERE? YOU TWO WANT TO LET ME IN ON THE JOKE?"
The other officer told him to lower his voice and watch his tone when speaking with a faculty member.
I finally got serious and explained to him it was an e-cig and how it worked, etc. Officer "new guy" asks to speak with the other officer and steps behind his car and they chat for a minute or so. Officer "new guy" then comes over and apologizes for raising his voice and I offered my apology for messing with him. We shake hands and he leaves. The other officer then slaps me on the back and laughing he says, "Doc, you gotta quit screwing with people like that"
I always have my ecig with me when I'm driving and I puff on it as I would a cigarette. I'm not trying to hide something I do that's not illegal. If I get pulled over, then I'll probably go through the same routine I did with the campus cop, unless the cop that pulls me over isn't a (phallic symbol) and tries to pull that "Billy Badass with a gun and badge routine" on me. I'm always getting some strange looks at stoplights when other drivers see me puffing on my Spinner. I usually just hold it up for them to see and I either get the "oh OK" look or the "what the heck is that look". A few have rolled down their windows to ask what it is. I just say it's an ecig and they are like, "Ahh". A few have even asked me to pull over and talk to me about it. I always carry some ecig vendor cards around with me that have my account number on them and my email address if the person has any further questions. I've had a few buy an ecig and I've gotten some credits on my Smokeless Image account.
So why hide your vaping if it's not illegal? Sure you may run into a cop or two that is suspicious, but that's their job to look into what they deem suspicious activity. The way you handle it is up to you. Like I said, if the cop is trying to be "Billy Badass" then he gets "the business", if he's polite, so am I. I treat others as they treat me, LEO are no different in my eyes, it's just all about how they come across. I've never been questioned by any other LEO about my Spinner or pulled over for it as of yet. But then again, the local cops where I live seem to be more interested in sitting along the interstate and pulling over speeders.