Special hood is not a nice look (5)
I believe the answer is:
scowl
'look' is the definition.
(I have seen 'dirty look' mean 'scowl' so perhaps 'look' could also mean 'scowl')
'special hood' is the wordplay.
'special' becomes 's' (common abbreviation as in Special Air Service).
'hood' becomes 'cowl' ('cowl' can be a synonym of 'hood').
's'+'cowl'='SCOWL'
'is not a nice' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for scowl that I've seen before include "Angry frown" , "Look angry" , "Glower; frown" , "Angrily frown" , "Gloomy or threatening expression" .)