Is the person behind you not entitled to comfort?
Your car is sold with a horn. Are you entitled to sit on it for 10 minutes at 3am in a residential area for no reason? Possibly. Should you? That’s the more important question when we live in a society.
Also if your father in law absolutely needs to use his laptop perhaps he should fly business class (I can’t speak to domestic services but internationally you’re guaranteed to be unaffected by others’ seats)