Impudence to staff is cosmetic (8)
I believe the answer is:
lipstick
'is cosmetic' is the definition.
(I've seen this before)
'impudence to staff' is the wordplay.
'impudence' becomes 'lip' (lip is a kind of impudence).
'to staff' becomes 'stick' (I've seen this before).
'lip'+'stick'='LIPSTICK'
(Other definitions for lipstick that I've seen before include "Cosmetic used to colour around the mouth" , "Cosmetic item" , "Colour applied to the mouth" , "Item of face makeup" , "offered to one's face" .)