In theory you should be able to use electronic cigarettes anywhere. However, that’s not the case as there are still bans and biases that bleed over from traditional tobacco smoking prohibitions.
There’s still quite a bit of unsettled controversy over e-cigarettes themselves too. Unfortunately, as their popularity increases, e-cigarettes have come up against some resistance from some authoritarian government agencies in various countries. The general theory among the vaping community is that e-cigarettes pose a threat to 2 very large industries with a lot of governmental clout…big tobacco and pharmaceuticals. They threaten the big tobacco industry for obvious reasons. As for big pharma, it cuts in on their lucrative NRT (nicotine replacement therapy) products such as patches, gum, lozenges, etc…and of course their highly controversial drugs like Chantix.
Part of the problem is that since e-cigarettes are so new, only a few credible studies exist so far, but that’s changing rapidly and many more studies are in process. As a result though, many of the decisions being made by authorities are currently based on lack of knowledge, fear of the unknown, fear of kids being attracted to it because it’s cool and electronic, or misunderstandings and twisting of facts. Rather than looking at how many people it can help, they choose to make decisions on unsubstantiated fear.
You can’t use them on many airlines and none in the US per the FAA. You may even find your local bar or restaurant objecting to their use. Probably the safest thing is to ask first! Also, take the opportunity to educate people where you can, and get involved in urging lawmakers to take a more sensible approach.
