With the two subsets of our population that aren't doing us any favors in terms of public perception (the cloud chasers on one hand, and the militant everywhere-vapers on the other), here's what I see as the main contributing factors:
1) The cloud chasers I've encountered tend to be very young; I'd peg the average at 20-21 and I'm certain I've never seen one over 25. When you're 20 you're still very much a kid, and kids get great enjoyment from doing things that outrage and horrify adults. If the average adult has a dubious view of e-cigs in general, then the obvious course of action is to walk around with a massive vaping device blowing obnoxiously huge clouds that earn you the dirty looks and consternation you so crave. Additionally, it's pertinent to note that if you put a group of young males together and give them an activity that can be turned into a phallus-measuring contest, that's exactly what they're going to turn it into. I freely admit that if I'd been born 20 years later, I'd probably be a cloud chaser too, and for these same reasons.
2) The militant everywhere-vapers are former smokers who still have a chip on their shoulder for all the years society spent turning them into social pariahs, and now they've found an avenue whereby they can, in their minds, get some measure of revenge for it. When you get right down to it, these people and their attitudes are an indirect byproduct of the last several decades of ANTZ propaganda campaigning, which succeeded in changing the popular consciousness to one in which smokers are perceived as contemptible, immoral, inconsiderate drug addicts who enjoy nothing more than poisoning innocent bystanders and small children whenever they get the opportunity. The resentment that smokers (and now certain ex-smokers) feel as a result is not at all unreasonable or unwarranted, but the members of the militant vape-everywhere crowd now think they're entitled to take that resentment out on the entire world around them, as though the scales of moral justice are somehow brought into better balance each time they blow vapor in someone's face "just because I can." Obviously, it's a misguided thought process, and one whose results reflect badly even on those of use who exercise courtesy and discretion when we vape in public, because people who dislike an activity are always more prone to base their entire opinion of that activity (and everyone who does it) on a worst-case scenario, which in this case is Mr. Militant Everywhere-Vaper. He just gives ammunition and affirmation to people who want to regard all e-cig users as slovenly bullies with no sense of social decorum.