If you were flying on an airline based in the United States, you violated their rules.
http://www.businessinsider.com/you-cant-smoke-e-cigarettes-i...
Beyond that, what gives you the right to put other people's health at risk? You have either judged them safe or decided you don't care about the risks. You can't make that decision for other people and you're not in a position to know what genetic or other disorders that someone might have that make them more susceptible to any kind of tobacco (ex: http://ghr.nlm.nih.gov/condition/alpha-1-antitrypsin-deficie...). How is this any different from me walking onto a plane with a clump of asbestos fibers and waving it over your head on the plane?