Hey, we all miss stuff from time to time. That's the thing about being human.
If he got that close why not stop pumping gas and take the nozzle out of the car? Then you can have your Zippo in hand and a questioning look on your face as you ask the possible adversary, "Can I help you?"
If he did have nefarious intentions you would have a good implemented protection device in hand. It also appears non-threatening to the other witnesses, and many wouldn't see the Zippo, but your nefarious individual sure would.
You do need to make sure that if this situation escalated that it would fall under the realm of deadly force in your locality, for you. Otherwise you will be the one doin' time and the "victim" will be collecting from you for life.