High-handed with regard to deportment (11)
I believe the answer is:
overbearing
'high-handed' is the definition.
(I've seen this before)
'with regard to deportment' is the wordplay.
'with' says to put letters next to each other.
'regard to' becomes 'over' (I've seen this in other clues).
'deportment' becomes 'bearing' (bearing is a kind of deportment).
'over' next to 'bearing' is 'OVERBEARING'.
(Other definitions for overbearing that I've seen before include "Officious" , "High-handed" , "Unpleasantly dominating" , "Forceful in character" , "Arrogant" .)