If you just be little discrete, and make sure you are not blowing clouds, there shouldn't be any problems.
I fly a lot, not only within the country but internationally as well. Vaping in the bathroom is the biggest risk, since if the alarm goes on, you wouldn't be asked any questions and penalized.
I always vaped on my seat, double inhaling, and the 3rd exhale on my shirt or directing towards the floor.
Never have got into any problem at all.