According to the papers cited about alcoholism and happiness, you are not affected by the behavior of your coworkers. For smokers, they only claim that coworkers influence each others' behavior within small firms, which makes sense because people are more likely to be friends anyway and there is more pressure to smoke socially. Even then, the confidence interval is huge; they claim smoking cessation by a coworker decreases your chances of smoking by 34% but with a 95% CI between 5% and 56%. I haven't read the papers, and maybe they explain this, but I wonder what happens when more than one of your friends stops smoking; surely they can't decrease your chances of smoking by 34% each.