A nail in somebody's/something's coffin - Idioms by The Free Dictionary
a nail in somebody's/something's coffin
(another) nail in (someone's or something's) coffin
Fig. something that will harm or destroy someone or something. (Alludes to the sealing of a coffin with nails.) Every word of criticism that Bob said about the boss was another nail in his coffin. Losing their biggest customer was the final nail in the company's coffin.
a nail in somebody’s/something’s ˈcoffin something, especially one of a series of things, which makes the failure or destruction of something more likely: If we don’t succeed with this campaign, it’ll be the final nail in our coffin. ♢ The new tax has driven another nail into the coffin of the British film industry.