We had a guy like this in the X-Wing community for a while named BRL. Would pop up every so often with a new name but he was pretty easy to ID once he opened his mouth, after which a ban would quickly follow. Lather, rinse, repeat.
Even had the same random IP issue preventing an effective perma-ban, too (although IIRC his was through AOL originally, so it's not like banning the whole kit and caboodle would'e actually been a real great loss to the community...)