Spare Cigarette - a mythical object

If you are a smoker you would have noticed how frequently you are asked for a Spare Cigarette. While most of my smoking friends willingly give away some cigarettes from their own packets, I never do. I know that this cigarette that I am giving away will be the very same one I will be cursing that I no longer have once cash runs out. It will be that cigarette that I will crave for at an ungodly hour of the morning when everything is closed. And above all it will never be a Spare Cigarette, it will be simple one of mine that I will not smoke.

It's unalienable truth: the cigarettes you give to people who ask for a Spare Cigarette are not actually spare, they are just regular charity. Spare Cigarettes don't exist in the real life and that's why when asked for one I always say there is no such thing. It usually just annoys people, because they really ask me if they could have one of mine and the question for the mythical Spare Cigarette is just simply so strongly embedded in English language that we have long forgotten that you could ask in any other way. Knowing that, I would ask "could I have one of your cigarettes" although in most cases when dealing with less picky people than me both ways would have the same effect.

I probably gave way too much thought to the subject of this mythical item, but I found that I can imagine exactly one situation in which regular cigarettes would become spare. Spare means something just in case, stuff that one has but won't use any time soon, stuff that one bought and doesn't need anymore. This would point to one realm where Spare Cigarettes could exist: quitters pocket.

Still, I have never met a quitter who would quit in the middle of a packet and even if they would they would not normally keep them in an attempt to avoid temptation.

So does a Spare Cigarette really exist or is it like Yeti: so everyone has heard about it but nobody ever saw one?