Intentionally team killing, not the first time either given their ban history.
Was definitely not sorry while doing it, most likely only sorry now that they've had a permanent ban thread opened on them.
This behavior is not ok on Ibis servers. It's not ok anywhere.
Taking an activity that gives someone happiness and taking that away from them is a horrible thing done by horrible people.
Blaming it on moods is a coward's way out, suggesting that you couldn't make a conscious decision to not be a dick because of a mood. If they're that powerful, you need to get prescribed something.

I would recommend a shorter, few hour ban, while adding a notice that if they are caught doing this again that a much more severe punishment would follow.