I don't see a problem with the carjacking. Just because the alignment is Lawful doesn't mean you have to obey the laws of the land. It means that you're a disciplined person who lives his life by a code. Could be to obey the law, but not always. If the Paladin is going by the Code of Chivalry, for instnace, then obeying the code trumps obeying the law of the land. Though I would suggest he not trash the car and that he leave it where it can be found so it can be found by the authorities and returned to the owner. And if not, copy down the license plate number and reimburse the owner for any damage done to the car.