Don't bother... no one wants to believe it. It is classified as the same disgusting habit as smoking and no amount of effort will change that. It never ceases to amaze me how able we are, as a species, to focus on things while ignoring other, much more serious, things. Like auto exhaust. Why? Because they want to go places so, that is OK. Bring on the exhaust, it won't hurt you, but, if I can see a "cloud", even if it's just water, that can't be good.
Still not as bad as those that so loudly call for smoking to be banned everywhere. It's not hard to tell the people that luckily were never addicted to nicotine. Otherwise, they might have a little understanding about how difficult it is to just stop. It can be done, but, so can running a 3 minute mile. That doesn't mean that everyone can do that just because someone thinks that they should.