Most of us have friends who are social smokers. They're the ones who don't ever take work breaks under the overhang with the smoking crowd, but come Friday, they're outside the bar having a butt or two as the night wears on. They rarely buy cigarettes because they don't want a whole pack; they're more likely to ask for a smoke from a friend. They never seem to get hooked and can go for weeks without even thinking about it. How do they do it when so many of the rest of us are hopelessly addicted?