Bad-mannered (4)
I believe the answer is:
rude
'bad-mannered' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for rude that I've seen before include "Unmannerly" , "Impertinent" , "Base" , "Ill-mannered; hearty" , "'Bad-mannered, discourteous (4)'" .)