Do nothing about contrary men (4)
I believe the answer is:
afro
'do' is the definition.
(type of hairdo)
'nothing about contrary men' is the wordplay.
'nothing' becomes 'FA' (slang term - sweet Fanny Adams).
'about' is a reversal indicator.
'contrary' is a reversal indicator.
'men' becomes 'OR' (military abbreviation for other ranks).
'fa' in reverse letter order is 'af'.
'or' reversed gives 'ro'.
'af'+'ro'='AFRO'
(Other definitions for afro that I've seen before include "Big hairstyle" , "Style of haircut" , "Curly hairstyle" , "Of hair style, tightly curled and bushy" , "Hair in tight curls" .)