I tend to assume griefing and shittalking in multiplayer games is roleplaying as a powerful character to forget one's own inadequacies in real life, where power structures can be harder to overcome. The bullied kid, the teen failing hard at school, the adult stuck in a demeaning job or under the thumb of others. ie. probably someone with poor social skills who is having a rough time and doesn't know how to deal.
So I warn/ignore/kick/ban them as needed, and move on.. they will either learn or they won't, but I'm not a social worker.