Exhibit poor posture (6)
I believe the answer is:
slouch
'exhibit poor posture' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for slouch that I've seen before include "Lazy and drooping posture" , "Slovenly gait or person (or hat)" , "Sit, stand or walk slovenly" , "Drooping posture - hat" , "Loll" .)