Walk the plank?

[Red Nations]

They could easily just log out, then back in on the same server.

True:
But they would not have your card open once they logged back. If they weren't on your friend list or the list on one of your crew members they could not TP back to you or your ship. My other idea of the "Allow or Deny" TP would completely solve the issue of unwelcome players teleporting to you in game. "The Allow or Deny TP" feature could be extended to give the captain the ability to control who can or cannot TP onto their ships even when boarding permissions are set to public.