I don't know. There's a character who, in canon, has kind of low self-esteem, gets agitated easily, and is kind of nervous. It's unknown if he's a smoker or not. So I had him smoke. Because most of my friends who are like that smoke to give themselves something to do with their hands, and often take up the habit in school because their friends smoke.

It made sense to me.

Also, smoking isn't any worse than alcohol, really. (Except to non-smokers) Do you get mad when characters consume alcohol when we have no idea if they do in canon?