Persona non grata from Latin- an unwelcome person.
This term is usually used in diplomacy, when due to some criminal/political actions a person is prohibited to enter a country. For example if a member of diplomatic mission is caught carrying out espionage missions he can be labeled "persona non grata", forced to leave a country and cannot return.
Persona non grata can also be used in less formal situation, when someone is not welcome in society/community due to his behavior.
You use expression by explaining your feeling in writing form. Sadness is one of the most expressed feelings in writing. Here is a site to get you an idea if you want to write a story:
https://www.scoopwhoop.com/saddest-lines-from-literature/#.fs19fnc37
Hope it helps!!!