another/the final nail in the coffin idiom
导致失败的事件，致命打击，催命符
an event that causes the failure of something that had already started to fail
Each successive revelation of incompetence is another nail in the chairman's coffin. 接二连三地显露出不称职是导致董事长下台的一道道催命符。
That report drove the final nail in the company's coffin. 那份报告为公司敲响了丧钟。