I smoke, and I don't care who knows about it. As long as I don't light up in smoke-free buildings, or in the homes or cars of non-smokers -- and I don't! ever! -- I feel it's no one else's business. I don't even ask a non-smoker if it's OK for me to smoke in their house or car, I just say "excuse me" and go outside for a few minutes. I even have a little "portable ashtray" I carry in my purse for such occasions (originally it was an Altoids tin) so I have a place to store the butts other than on their lawns.
So when people make unsolicited comments about the fact that I smoke (yes, it happens every now and then), I don't let them give me guilt trips over it.
And yes, I've heard it said that non-smokers can supposedly "sniff out" smokers, even when the smokers aren't smoking in their presence. I still don't care, because in my opinion there are worse things to smell than traces of tobacco odor on someone who has regular personal hygiene habits (i.e, takes showers, brushes teeth, wears clean clothes).