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（因行為令人震驚或反感）大家唯恐避之不及的人，被排斥的人
If you refer to someone as a leper, you mean that people in their community avoid them because they have done something that has shocked or offended people.
例句
The newspaper article had branded her a social leper not fit to be seen in company.
報紙上的這篇文章給她冠以“社交毒藥”之名，稱人皆不宜與其為伍。