They just use the internal tools and create a ticket to have an admin ban your IP and all current and future accounts. Wow, such a hurdle!

Even more awesome to have this happen with a dormitory IP. /s

Yes, they can. If you piss off a moderator they'll just ask an admin to ban you, assuming it's not an admin's alt in the first place (admins have sockpuppet mod accounts on every major sub)