what would you tell him?

I extremely hate smoking and that's the fact, but as much as possible I want to be tactful and courteous when dealing with other people's inconceivable manner especially in public. I often caught people smoking in a non-smoking area and I would often wonder if they were in their right senses doing such ridiculous habit in a prohibited area. Every time I encounter this situation, I would glare them, shut them a spooky look and darted my eyes in the horizon, lol! Sometimes I would held my breath when surrounded with smokers because I am afraid of the second-hand smoke effect, this is more fatal than direct smoking according to health experts.