There's only one rule to know about vaping in public, especially during this peak travel period: There is no one universal rule. Policies differ by industry, and sometimes within the same one.
Most airlines do not permit the use of e-cigarettes on board, but they do allow users to pack their batteries and juices in carry-on baggage. (Bear in mind that TSA regulations on liquids apply.) Most major American airlines—including United, JetBlue, American Airlines, Delta and Southwest Airlines—ban the actual act of vaping in flight, as do many international airlines like British Airways and Japan Airlines. Although it may be tempting to "sneak a vape," take this as a warning: You don't want to be the person who gets caught and makes an entire plane turn around.
It's not just airlines either. Amtrak also forbids e-cigarette use. In general, transportation services are strict about anything related to smoking.
Hotels may be another matter, considering some still have smoking and non-smoking rooms. But every operation is different. For example, I've stayed at many bed and breakfasts, hotels and motels that met my vaping behavior with keen interest, not loathing. However, it's worth noting that none of them were a Marriott. The hotel chain charged one Chesapeake, Virginia woman $250 for vaping, citing the hotel's anti-smoking policy.
The rules are even harder to pin down for restaurants, bars and cafes. Even though nicotine and caffeine are an infamous match, Starbucks doesn't permit e-cig use. Restaurants can be equally testy about the activity, as well as some bars. But not all of them. Mark Birnbaum, co-owner of EMM, Group which owns clubs like FL and Finale, likes that that they don't encourage customers to leave the premises. “It’s hard enough for us to get them in,” he explained to The New York Times. “Then you’re forcing them out on the street to smoke.”
But many businesses don't share Birnbaum's sentiment, so it's a good idea not to make assumptions. Common sense prevails. Vaping is allowed anywhere smoking is. As for everywhere else, remember that the rules vary. When in doubt, check. It's a simple step, and it could go a long way in putting people at ease—which is exactly what you want while you're on vacation.