It'd be pretty hard (if not impossible) to prevent said person from being on a team and getting in. You only really have control over the general base permissions (members only, etc) and I 'think' changing the base code would work like changing the locks, but then you could never put that in the Base Codes thread, etc.
Beyond the "breaking the RP vibe" type stuff, unless they're somehow being abusive (aka: against the TOS), then there's not much beyond the /gignore you can do. Even if you Did this as a group, then you'd have to look-up every PUG based team mate that you join with...ever. Now THAT's a headache right there.