The purpose is to help the addicted user stick to a decision to concentrate on a different, short-term real-life problems s/he urgently has to deal with.
I've seen this feature on some high-activity community forums. "Ban myself" button should offer several pre-defined periods for banning: starting with a few days, and up to 2 weeks (or maybe even a month, but that seems too much).
Optionally, this button should ban the requesting user on all profile-linked SO sister sites.
Clearly, there should be no way out of self-ban period.