First of all how does he get past you, or into the drivers seat when your standing right behind the opening of the drivers door while monitoring the fueling of your vehicle? At least that is where all the fuel doors are on my vehicles.
Second how are you going to shoot him when your rolling around the back of the truck with your gun in your hand? You tap on the glass to show him you have a gun, and he slams on the breaks, now your eating the back of the cab, then he steps on the gas, and starts to turn etc. Not the best place to be with a gun ready to shoot.
Third, I don't buy the wear and tear thing on the diesel engine when it is already warmed up from running. Everything is already lubricated from the drive to the station. Sure cold starting wears on a motor, bearings etc., but after your drive to the station it ain't going to matter.
So bottom line is, I turn off my vehicle when fueling, and put the keys in my pocket. If someone was to happen to get into my vehicle and get it started, I would not just in the back of the truck and attempt the tap on the glass thing before trying to shoot them. Why not just stand their and shoot the tires out from terra firma. :rofl: (no I would not shoot my own tires out)