Anyhow, he continued being incredibly abrasive and angry until our supervisor called a meeting and he claimed that he had aspergers - which may have been true but it effectively tied the hands of my manager. They explained to me that they could not let him go even though it would be best for the team, because he had made this statement and there could be legal troubles if they did.
So he continued on being toxic, until he blew up in a PR review (basically left an insane set of GitHub comments) and they decided this was too much and they moved him to another project/team where he would have very little interaction with people.
Anyway just wanted to leave this as an anecdote for a situation where the solution was very difficult to solve and eventually it was sort of solved but it definitely required managers giving feedback about someone’s personality.