Don't leave your car running while filling it up.

1: your car can get stolen

2: you or someone else might drive off with the pump still plugged in because you forgot a step. (Especially if you hop back in the car to stay warm in cold environments)

3: it is a fire risk.

The employees should have stopped you from filling up if your car was still running, in the same way they could if you were smoking, but the employee is completely out of the loop as most transactions are automated with a card, and also gives zero f+++s