Caustic quip by well-mannered man? (7)
I believe the answer is:
pungent
'caustic' is the definition.
(I've seen this before)
'quip by well-mannered man?' is the wordplay.
'quip' becomes 'pun' (I've seen this in other clues).
'by' says to put letters next to each other.
'well-mannered man?' becomes 'gent' (I've seen this in another clue).
'pun'+'gent'='PUNGENT'
(Other definitions for pungent that I've seen before include "Strong-smelling" , "Sharp tasting/smelling" , "With a fifteen ac smell/taste" , "Biting" , "Offensive" .)