[tacostakohashi]

Provocation is a thing, e.g. reducing murder to manslaughter or 2nd / 3rd degree murder if the victim provoked the attacker first somehow.

Self-defense is a thing, it's sometimes reasonable to attack a person before or while they are attacking you.

Retribution is not a legitimate grounds for assault, that's what the justice system is for.

Your example is light on details, but if it's just retribution without an element of provocation / self defense (e.g. B punches A one year after A punches B), then there wouldn't be a reason to dismiss such a case.

As for your conversation, one principle in any organization is to remain polite and professional at all times, even (and especially) when other people are not. If a conversation is "going nowhere", telling the other person that they are "difficult to talk to" could be a legitimate observation or constructive feedback. Management have no interest in analyzing the rights and wrongs of such situations, they only care about who acted professionally, and not about the order and reasons behind such behavior.