Auto Insurance Claims: Parking Lot Accident, Who is at fault?, parking lot accident, morine

Question

I was at my school parked in a parking spot where I did not have to back out and there was a truck parked beside me and he had to back out. his driver side faced my driver side.
I had my door open about 10 inches to stick my head into my door and tell a passenger somthing. my body was between my car and my door. The white truck beside me then backed up and cut too soon and hit my door in the part where the center is. and it left a white line vertical to show where he hit my door. He said my door was WIDE open but if that was the case he would have scratched the inside of the door up but it only left the mark on the edge and outside of my door. He wants me to pay $500 because he says my door was over into his line but I know he swung into my door and my car wasn't even running and no one was even in the drivers seat of my car.  

Answer
Generally speaking, whoever took the "action" last has the duty to exercise caution and yield to the object already present.  They had the last clear chance to avoid an accident.  

If you are both in agreement that your door was open first, then he had the duty to wait for you to remove the obstruction (the door) from his path before attempting to operate his vehicle.  Just because your door was over his line does not give him any legal right to strike it with his vehicle. You can explain to him that if his logic were true, then he would have the right to also run over and kill any pedestrian that happened to be over the line as well and we all know that would never fly. The lines are only there to give people guidance on where to park.  

If you cannot agree on what happened first, the open door or his moving of the vehicle then each party will end up responsible for his own damage.

Good luck!