If you are a true professional, you MUST be able to refrain from smoking onboard. As professionals we must put up with much worse restrictions than not smoking!
I smoke cigars since 7 years, before I used to do a pack and some a day. I stopped smoking on the deck since more than 5 years. I do on the average 10+ hours sectors. I don't even let my wife smoke, when she's along.
My first reason is it is not fair to other smokers on board. Forget rules and regulations. We, on the LHS, are not God to have the privilege of bending rules and embarrassing pax and colleagues.
I pity the guys that do it!