Yes.
This is the other side of the story and I'll let everyone decide who is right
It was on the CDG-TLV leg.
PAX asked a FA politely if he can help him switch, to which he replied with attitude that he can either sit in his seat or get off the aircraft, they started arguing and at some point the FA told him "you can fly elal if you wants this privilege" and just walked away, so he went and sat down in a empty fake J seat. FA came to PAX again and said "you have to pay for this seat" so PAX offered to pay but FA refused. At the end they moved someone else from Y to J and he got that seat.
Sitting down in a cabin you didn't pay for, is totally unacceptable IMHO, and it's יצא שכרו בהפסידו
I agree with you that he shouldn't have sat down in j, but then again אל תדון חברך עד שתגיע למקומו
I can understand him for getting annoyed as I can believe the full story as I've seen this exact same scenarios in the past, when people ask politely and the flight attendant answers with an attitude.
I'm sure we'll have some (anti-semites)[clear minded people] bashing the passenger...