2PHRASE 美中不足之处;败兴的人(或事物);煞风景的人(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. 美中不足之处;败兴的人(或事物);煞风景的人(或事物)
Rachel seems to be the one fly in the ointment of Caroline's smooth life.