I smoked, very casually, while in college. Never did get a hook in me, which I'm thankful for.
BUT...and this is for all the smokers out there...I ended up with a rare genetic deficiency that resulted in a rapidly progressing form of emphysema.
Alpha-1 Antitrypsin Deficiency. Usually not detected until mid-life (I was in my 30's). http://alpha1.org/
I went from running hoops with guys half my age to on oxygen, 24/7, in the space of about 5 years.
You have no idea what it's like when your lungs are shutting down. Imagine the most out of breath you've ever been...the scary out of breath...and think about having that desperate need for air all the time. Slowly walking across a room. Bending over. Sitting.
I ended up having a double lung transplant after nearly dying, and am in great health now. My chest hurts ever day from where they sawed through my sternum and wired it back together. I have to take 30 pills a day to guard against rejection, which can h=appen at any time.
Oh, smokers? If you get that sick, they usually won't give you a transplant. Odds of you slipping back into smoking are too high. At best you'll get one lung, which isn't much of an improvement.
I spent my first 25-30 years of life basically ignoring advice given to me. Was pretty sure I knew everything anyway. But if you listen to only one thing in your life, listen to this.
Don't smoke. If you do, quit TODAY.
Good luck! Don't let anyone convince you it's too hard or not worth it. And whatever works for you is the right way to do it.