PHRASE
美中不足之處；敗興的人（或事物）；煞風景的人（或事物）
If you describe someone or something as a fly in the ointment, you think they spoil a situation and prevent it being as successful as you had hoped.
例句
Rachel seems to be the one fly in the ointment of Caroline's smooth life.
蕾切爾似乎是卡羅琳一帆風順的生活中唯一的麻煩。