Depends on how bad it is.
A social smoker would fit into the "mild" category: they're probably only lighting up on the weekend when they go out to the bar.
An average smoker would probably be mild: they're known to smoke, you see them smoking, but they're not the person who's getting up every hour to go out and light up.
Then you go into the severe category: at this point, the smoker is going out every hour to light up, their clothes always smell of smoke, and they've got tobacco stains on their teeth and burn marks on their clothes.
Finally, you go to burnout: At this point, the phrase "pack-a-day" is in the past. The typical chain-smoker: just spending a fraction of an hour without a cig is enough to make them antsy. They're happiest when their lighting their next cig off the butt of their first... while they're still smoking it.