How do you get banned from twitter?
If you troll hard enough, and long enough, and enough people "report you" they'll suspend your account for a few days. If you continue long enough through multiple suspensions, apparently they'll just ban your account altogether.
Clearly one can resurface under a new guise, however they dropped the perma-ban on ol' Biff last spring after an all out retaliation by KiV and her minions.