Every Forum creates and agrees to a Code of Conduct between the members. If a member repeatedly violates various items within the Code of Conduct, they are removed from the Forum. From the point of removal, there should be a 60-day (or 2 meeting) cooling off period, in which the violating member is typically not allowed to re-apply to join the group.
The reason for the cooling off period is that it gives everyone a chance to step back from the emotions of the situation before taking any action. The violating person gets time to reflect on if they can actually commit to the Code of Conduct. The rest of the group gets time to reflect on whether the violating person is actually a good member for the group.
Without the cooling off period, I’ve seen a member violate the Code of Conduct and quickly get voted right back into the group. In this case, the Code of Conduct loses its value. Lack of strong commitment to a Code of Conduct is a big red flag that a Forum is failing.
After the cooling off period, the violating member can ask the group to rejoin. Just like with new members, there needs to be unanimous approval from all the current members for someone to join the group, even if they were previously a member.