Charles
Mounted Parthian archers were trained to continue firing arrows into the enemy while in real or feigned retreat, creating the obvious military advantage. "Parthian shot" has come to mean any "last words" or attacks fired by somebody who claims to be leaving the scene.
As for your phrase: hmm, if the phrase is as I assume from your allusion to music, then it presumably refers to an unacceptable prerequisite or association as discovered by both Bach and Handel. Nice!
This is getting like Trivial Pursuits!
Regards
JR
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1