I always carry disposable plastic tips in my pocket that I ordered through a health shop (I'd imagine they could also be picked up at a head-shop or pharmacy supply house).
If I remember correctly, they were about $10.00 for 100 of them. And being that they're individually wrapped and not too large to carry a couple around in my pocket they are perfect for "those" situations when someone actually wants to try it.
When someone makes the motion or asks to see it, I'll pull the tip out of my pocket saying "if you'd like to try it, here... use this", which they then understand what's expected of them. If they don't and try to take a vape they would get a smack to the head as their reward for ignorance (so far, so good, no schooling required, lol).
I don't consider it a case of OCD nor unrealistic expectations to demand common courtesy and personal hygiene from others as a "normal" person would of me, and especially at a time where illnesses are rampant in the general population through uncaring and negligent behavior.
That's what I do, and it works great.... a simple precaution, and an inexpensive one to boot.
VapeOn,
Greg