Coup De Quoi?

The copy-editing dept, i.e. you, has sent me a memo. "Coup de grace" means a strike that tries to put a victim out of his or her misery. It does not mean what I wanted it to mean in this post. A reader elaborates:

If Cheney had been killed in the attack it might have been the coup de grace to the administration's policies in the region. The attack may have been a coup de main; it was certainly a coup de theatre.

Obviously not my coup of tea.