The way I see it, the majority of Thais don't give a rat's <deleted> what you're smoking or where you smoke it and you'll only feel heat if you're caught red-handed by the BiB.
I smoked a joint last week at the DMK Terminal 2 smoking area and didn't attract any attention, whatsoever. Obviously, I didn't pull out a 12" reefer and wave it about (it was only slightly longer than a cigarette) but there's obviously no hiding the smell and plenty of airport workers were there as well. All was fine.
What I personally wouldn't do, for example, is smoke weed walking along Sukhumvit and if I did need a smoke, then I'd find somewhere to stand away from the pavement and where there's little chance of the BiB jumping out from behind a lamppost. ????