Persona non grata

The phrase means "unacceptable person" (in Latin). The usual usage is for foreign diplomats who, for some reason or other, have become unwanted by the host country.

The usual reason is that the diplomat has committed some crime (perhaps espionage, perhaps something more mundane). Diplomatic immunity may prevent them from being jailed, but it doesn't mean the host country has to let them stay. They're declared persona non grata and kicked out.

This also sometimes happens in war at a blanket level, where all the diplomats of the enemy nation will be kicked out.

It's also used in a semi-humorous way for someone who is getting the stink-eye for some reason: "After Debbie's boyfriend broke her mother's vase, he became persona non grata in the Miller household for months."