Do you not recognize that you are treating vaping exactly like you treated smoking?
You are assuming the default position that what you are doing is as offensive to others as smoking.
You are not a smoker. Shed your smoker mentality.
If we all keep acting like we did when we were smoking, we will be treated the exact same way and, frankly, we'll deserve it.
There are some places where it might be appropriate to ask permission in advance, but in most public settings, excepting maybe restaurants and a few others, it's not.
Vape in public. Wait for someone else tell you that it's wrong or ask you to stop. If they're not the owner, or even if they are, ask them why. They'll have no reason based on any fact whatsoever. That will provide you with the opportunity to enlighten them. If they refuse to listen, they're being irrational. If they own the place, then fine, comply. But if they don't, you have no duty to bend to the will of someone who is irrational. In that case don't feel guilty or like a militant when you tell them to go pound salt.
Uhm, no, just no.
Look, i live in Germany. We recently got a ban on smoking in public areas like bars, restaurants, but not in the open air. Smoking had been already prohibited in public buildings like youth clubs, churches and the likes even before that.
Bars, clubs and restaurants can(!) allow smoking, IF they have a separate smoker's compartment that is away from the nonsmokers' area and as long as the nonsmokers' area stays separate from the smokers' compartment.
A store(!), on the other hand, is not "open public", neither is a bar, pub, restaurant. At least not legallese-wise if it comes to trouble. If you misbehave in a store, bar, pub, what-other-locale-of-your-choice-you-ever-choose in any way the owner deems inapropriate, the OWNER and/or his/her seconds can either kick you out themselves, or they could call the German police to have(!) you kicked out of the locale.
But going back to the matter of vaping. I vape in public, on public places, on the street, in a park, whereever i like.
BUT:
It's a matter of respect towards the place's owner to ask for permission in an enclosed location beforehand, not a matter of "I have to explain my vaping". That's nonsense on your behalf.
Why i do ask for permission, though? Because even if i can reason with most people here in Germany, vaping without permission in a place where it'd be frowned upon or outright illegal to smoke seems to people uneducated about vaping like a perceived violation of smoker's ban. They see a cloud of white stuff and perceive it to be smoke.
Vaping is NEW to the folks here in Germany, hence why most think that i'm still SMOKING, but actually i'm vaping. Add that to the fact of trying to fight more and more rampant lobbyist bull.... anti-vaping propaganda blown from German mass media to disinform the masses and you might understand why RAMBOing our vaping into other people's faces is not the best idea, even if we Germans are rather (negatively) known for our bluntness and direct actions.
Am i clear now?