Cold turkey.
A guy I work with moved to Chicago from Nashville last year, and he's a pretty okay guy. Last week, he quit smoking and we're all (meaning me and my fellow coworkers) trying to be really supportive of him. However, and as could be expected, he's in a terrible mood after six days of no smoking and is biting the heads off of everyone he goes near today. I've decided that the best way to handle it is just to not say anything to him at all, and let him stew in his own juices.