Persona non grata is a person that is in disfavor, who isn't welcomed or whose presence is not desired.
An example of persona non grata is the black sheep of the family who has been told never to come back to Thanksgiving dinner.
An example of a persona non grata is a diplomat who is unacceptable to his home country.
Fully unacceptable or unwelcome, especially to a foreign government.
The diplomat was persona non grata.
A person who is not acceptable or welcome; esp., a foreign diplomat unacceptable to the government to which he or she is assigned.