Never in bed, or in a queue, and certainly not in a restaurant - the fog may have finally cleared on the rules of vaping in polite society.
There are now more than 2.8m e-cigarette users, or vapers, in the UK, according to official figures.
Yet many still don't know where or when they should vape - with more than half of those surveyed by e-cigarette brand Vype complaining they were "baffled".
Now etiquette experts Debrett's has issued its own rules for acceptable vaping.
Though vaping is now well and truly mainstream, Debrett's says that "a lack of official guidelines doesn't make vaping universally acceptable".
The main reason people vape is to give up or cut down on smoking, according to Public Health England, but non-vapers aren't always sympathetic.
The e-cigarette brand Vype carried out its own survey of 2,000 people to identify the biggest faux pas for vapers - and found that vaping in confined spaces, such as a lift, was the clear number one gripe.
This was followed by vaping in a restaurant, during a job interview, in someone's face or in someone's car without their permission.
Other unacceptable times to vape included vaping in a queue, in someone's home without their permission, on public transport, while someone is cooking and, finally, vaping in bed.
Separately, Debrett's has issued its own guidance, saying the rules on vaping are "largely discretionary" - which leaves vapers taking on a "social minefield" armed only with good manners.
Debrett's rules of vaping etiquette
Do ask first - most public places like bars or theatres will have clear policies, but if in doubt - ask.
Do hint to other vapers if you want to sample their liquids for a change in flavour - but don't ask them to share the e-cig itself. Most vapers will stop short at sharing their mouthpieces.
Don't puff away in a restaurant. Most restaurants have a clear no-vaping policy while food is being served.
Don't vape in a queue - consideration for others is key here - no matter how tedious it can be waiting in line.
Don't assume that if you are in a friend's house or car you can vape - ask first. It's polite to take it outside.
Don't blow vapour into someone's face - while you may enjoy emitting huge clouds of sweet-smelling vapour, not all non-vapers will appreciate it.
Don't vape on board buses, trains or planes - most ban vaping, so accept it with good humour and take advantage of the smoking areas if you want to vape.
Don't assume that hotels allow vaping - better to check when you book.
Don't attempt to discreetly "stealth vape" in vape-free zones - it's best to wait until you can vape openly.
Don't be shy of romance with non-smokers - according to Debrett's research one in five of them would happily date a vaper. That's five times the number who would consider a date with a smoker.
Deborah Arnott, chief executive of health charity Ash, says organisations need to be clear on the differences between vaping and smoking.
She argues that vaping is a "matter of courtesy on both sides".
She said: "Vapers should use common sense and not vape in crowded or confined public places, but they shouldn't be made to feel uncomfortable or apologetic for vaping.
"They [non-vapers] should be mindful that the e-cigarettes are used largely by current or ex-smokers to quit or prevent relapse back to smoking, and that e-cigarette vapour does not deliver the toxic load found in tobacco smoke."
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As for the law, the government views vaping very differently to smoking - therefore the smokefree legislation does not apply to vaping.
Though it is illegal for under-18s to buy e-cigarettes, there is no penalty for vaping in the workplace or in public places, on public transport, in restaurants or bars.
Instead, it is left up to the company or owner to decide.
While the debate continues about their level of safety, the Department of Health's consensus is that e-cigarettes are "significantly safer" for users than smoking tobacco.
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