I don’t like it for many of the same reasons I’m not fond of cigarette smoking - I don’t like the smell. I don’t like having the smell sticking to me and my fabric goods for the next X amount time, either. Yes, it has a smell. It has a myriad of different smells, actually. Some of them are okay, but I’m not fond of artificial aromas in general and some of them have been known to trigger migraines for me. Some are stronger than others, and therefore more annoying.
I feel about vaping the same way I feel about sharing an elevator with the lady from the 12th floor who apparently feels as though marinating in perfume is necessary and appropriate. Or, for that matter, the way I feel about the lady at the grocery store last weekend with the three year old who was screaming (not like hurt, just crabby because his mother didn’t want to get him the toy/candy he wanted and his choice of persuasion was a twist on the “I’ll hold my breath until I turn blue” technique - namely, screaming until he ran out of breath and then gasping in a huge breath and diving in again. He kept it up for the entire 20 minutes I shared architecture with them. Good lungs on that kid. Mom ignored him.).
It’s a mild irritation, a minor inconvenience, and (since vapers are, by definition, doing on purpose) mildly inconsiderate.
Because it’s a mild irritant, inconvenience and inconsideration, I rarely bother asking people to stop doing it (unless they want to do it in my own personal space - car, house, at my desk at the office) in public. That does not mean I don’t notice and wish to myself they’d knock it the eff off. If I fart in public - or have a nasty cough - I apologize for producing a mild irritant/inconvenience/bit of inconsideration. Good manners, and all that.
I’m sure there are considerate vapers - there were (and are) also considerate smokers. But puffing away at seated at a table in a restaurant (I want to smell the FOOD, thank you, not your mango/pina colada/chocolate/minty/tobacco/strawberry-wtf-ever vapor smell) or on a bus or train (where I’m trapped in with your smelly compulsion whether I like it or not) is inconsiderate and flat-out rude. Do your vaping before you get on the goddamn public transit - or step outside away from the door of the restaurant.
The whole question of whether or not the vapor emitted is safe for general consumption is one about which we don’t have any actual research (which isn’t really possible given that there currently exists to my knowledge - and perhaps I’m mistaken - no regulation or oversight of what goes into the liquid used). In the absence of any actual concrete information, I have a hard time blaming people who’d rather be cautious about what they’re inhaling. It doesn’t have anything really to do with why I, personally, don’t like it, but I understand the viewpoint. It’s not an unreasonable viewpoint by any stretch of the imagination - half of the containers of vaping liquid I’ve personally seen don’t even list ingredients. Or they say things like “X% nicotine and X% inactive ingredients”. It was largely the “inactive ingredients” that made cigarette smoke unhealthy.