I did this once at my local convenience store. The person tracked me down in the parking lot and asked if they could bum a cigarette. I said I don't smoke and then they walked away. I am thinking they did NOT pay it forward. I questioned my intentions and then still felt good enough to try it again at a toll booth. At least there I am in my car and can floor it so they don't catch up to me to ask for smokes. lol