Ill-mannered person left exposed (4)
I believe the answer is:
lout
'ill-mannered person' is the definition.
(I've seen this before)
'left exposed' is the wordplay.
'left' becomes 'l' (common abbreviation).
'exposed' becomes 'out' (out on display).
'l'+'out'='LOUT'
(Other definitions for lout that I've seen before include "Ruffian" , "Ill-mannered youth" , "Antisocial person" , "Boor, oaf" , "Awkward and stupid person" .)