I must admit, I'd be very tempted, in such a case, where the parents are clearly entitled to claim the son, to file their return, before doing his, and, in fact, before even talking to the son. Then, I'd transmit the return, THEN turn to the son and prepare his as the dependent he clearly is. Then tell him he can not claim himself, because he has already been claimed.
But when parents let their kids walk all over them, as this one's attitude makes clear he does, [a smart parent would pull the keys, I bet this one pays for the kid's gas, insurance, etc.] it's not our place to play family councilor. I agree with MAS that the kid SHOULD be willing to help his parents at a time of their need, given all they do for him, but no doubt they taught him to be the selfish oaf he is.