Coup de grace

[Britney]

This phrase means blow of mercy in french, and is used to describe the deathblow intended to end the suffering of a mortally wounded victim.
It can also be used figuratively to refer to a finishing touch of any sort.
While the correct pronunciation is similar to coo de grahce. It (in english) is usually pronounced as coo de gra...with the final s sound being left out.

[PussyCat]

To achieve complete, argumental dominance in its most pure form. Once a coup de grace is tactfully executed, the executing individual terminates/wins said argument. If performed... No can defense.
Any of the following may be used:
Its science...
Except when its not...
Well.. Not on this earth. Respectively.
NOTE: Coup de graces may not be utilized in tandum and/or against one another in the same argument.