Most impolite (6)
I believe the answer is:
rudest
'most impolite' is the definition.
('rude' can be similar in meaning to 'impolite')
This is the entire clue.
(Other definitions for rudest that I've seen before include "Most bad mannered!" , "Most vulgar" , "Most unrefined" , "Least polite, most unmannerly" , "Most ill-mannered" .)