Idiom: (a) nail in the coffin / or a nail in someone/something’s coffin
A coffin (see picture) is a long, narrow box in which a corpse is buried. A coffin is often made of wood.
To close a wooden coffin, nails (small metal spikes) are usually hammered into it. So the final or last nail used would completely close the coffin. At that point, you're dead, cannot get out and are ready to be buried in the ground. This is obviously a very final state to be in.
— My latest injury put another nail in the coffin of my collegiate football career.
— If I get another poor grade in math it could be the final nail in my coffin.
— Getting caught for underage drinking was the nail in the coffin of my college scholarship.
— New tariffs on steel will be the nail in the coffin of our company so we are protesting this proposed ruling.
— The witnesses testimony was the final nail in the coffin for the defendant's case.
— The latest plane crash in Ethiopia is the nail in the Boeing 737 Max aircraft's coffin.
— If you're late one more time, it'll be the nail in your coffin.
— Any allegations about sexual harassment, whether true or not, will be a nail in the coffin for your political campaign.
— This speeding ticket is the nail in the coffin of your driving privileges. From now on, you can take the bus or ride your bike.
— Getting convicted for manslaughter while drunk driving was the nail in the coffin of my legal career.
— Cheating on my wife was the nail in the coffin of my marriage.
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