I am a flight attendant for a major airline and I would say most flight attendants do NOT know about e-cigs. A passenger approached me several months ago asking to vape on one, before I knew anything about them, and my colleagues and I said no way!
Without going into long boring detail about federal airline regulations, airline policies, ad nauseum, let me just say that you are probably not going to get a good reaction trying to vape on a plane. I'm not agreeing with it, it just does not bode well to try it. When e-cigs become more of a common knowledge thing it may change, but I'm not betting on it. People just get too freaked out with anything even resembling smoke, and the airlines are not going to want to deal with it. It's kind of a least-common-denominator thing--when in doubt, leave it off. The airlines have banned those personal air purifiers that hang around your neck as well as self-heating meals, so I seriously doubt they'll ever accept the use of PV.
All that being said, feel free to vape in the lavatory where no one can see as long as you make sure all the vapor is gone before you open that door, but you didn't hear that from me!!
