Looking cool. For real though smoking (anything) has to be the dumbest thing ever when you stop and think what your lungs are, everything they do for you and how you "repay" them for their kindness of being able to sit there reading this whilst breathing.
On a larger scope, from a Chinese medicine point of view it pushes bioenergy downwards which helps keep things under the surface - see stressful situations and relapsed smokers.
Psychologically it can relate to issues of childhood security that haven't been addressed and things like suppressing appetites.
Random fact, did you know that the cigarette industry is the second largest user of sugar behind the processed food industry? Its also one of the few things you can buy to consume that doesn't have an ingredients list on because if people saw things like Arsenic, Ammonia, Formaldehyde, Methylamine, Acetone etc.. it may just make them think twice about lighting up.