I smoke about a pack a day, I know shouldn't and I'll add another "trying to quit notch" on my belt shortly, hopefully it'll stick. I'll finally do it eventually, but it's an addiction like any other. I'm sorry I ever picked the d@mn things up, but I did. I stay away from the non smokers when I'm smoking one, I don't smoke inside (even my own house) and I don't blow smoke into anyone's face (or any other orifice).
Half the guys on our staff chew though, it's a big thing on our crews. I normally don't see people doing that anymore, but there's at least 10 medics I can think of off the bat that chew tobacco.
Smoking on the rig? That's a big no no for a reason, those O2 tanks and fire are not a good mix.