Coming from someone I'm with, just about any kind of request to refrain from smoking would work on me. Coming from a stranger in public, it would depend on the situation. If I were outside I might refuse, but a polite and friendly request would be most likely to work.

I usually vape these days, but people even complain about that sometimes.

The person making the request could say they suffer from asthma or some sort of respiratory illness and couldn't be around smoking.

I'm not sure why the question, though. Smoking is prohibited indoors in all establishments. So, there's no need to reformulate a request, just say smoking is not allowed here, please.

I've never been asked not to smoke, but living in a big city, I would probably just move far enough away from the person and continue. As the Elephant mentioned, I'm not sure why you asked the question.

It's about neighbors and coworkers who smoke (at work or in break).

I open the windows in the morning to get some fresh air, and what do I get? The odious smell of my neighbors smoking.

While in the country where I live smoking is prohibited indoors in most establishments, many people ignore that. If I were to say "smoking is not allowed here, please", then, in the best case scenario, I'd get laughed at. (Not to mention that there are not just a few non-smokers who will jump to the defense of smokers.)

I usually vape these days, but people even complain about that sometimes. — Jamal

Smokers tend to have a diminished sense of smell. They can't tell how bad the smell from smoking is.

It's one of the reasons why it's useless to talk about it with them. They can't relate.

The person making the request could say they suffer from asthma or some sort of respiratory illness and couldn't be around smoking. — L'éléphant

And get laughed at or told to leave.

Unfortunately, a noxious personality is much harder to give up than smoking.

Back somewhere around 2004, breathing air in New Delhi was equivalent to smoking a packet of coffin nails a day. So yeah....smoking, breathing city air, it's the same thing, bruh!