Can I smoke one cigarette while out this weekend?
Cigarettes are so unhealthy, why would you smoke one?
I might die without it so I'll smoke one.
It's the weekend, so I understand that you want to kick back and relax, which is fine.  But you should find a better way to do so, one that doesn't involve hurting yourself or others.  Kick the habit!
I'm going to do what I want to do.
Smoking one cigarette can lead to an addiction that will cause you to want another and another. It's best to relax in a way that will help you instead of damaging your health.