, especially "formal and rarely used". In the plural I've only ever met it in the context of diplomacy. In the singular it's slightly more widely used, but still formal. If a man is told by his wife 'Get out - you're not welcome any more' he
might report the words in a formal deposition (e.g. sworn statement to be presented in divorce proceedings) as 'She said I was
persona non grata'. But most people can get through life without using the phrase at all.
b