Conflict in the on the ground before flight should mean the flight will not take place unless those causing the the conflict have been removed beforehand. In the air, it is up to the crew to make sensible decisions. The responsibility of ensuring good order and conduct etc. rests with the Captain. After the flight the local national laws, both civil and criminal, apply and the flight crew simply become citizens.
The pilot in that clip did well not to react. I don't know whether or I could do what he did. Unfortunately, whenever you have your uniform on you become a target for a considerable number of idiots, like the one in this clip. I do hope he pays the price first for assaulting another person.