Smoking is not a hobby.
Hobby is a kind of activity that you do during your free time and it happens intentionally. Smoking is an addiction which is harmful for your health. Hobby can be doing sports or collecting something or something else. Smoking, taking drugs, drinking alcohol are not hobbies, but serious addictions which should be delt. Hobbies help people forget about their troubles and swich their attention from working issues to something else and they help them recharge their batteries and broaden their outlooks.