Stupid person wearing short coat (6)
I believe the answer is:
jerkin
'short coat' is the definition.
(I've seen this before)
'stupid person wearing' is the wordplay.
'stupid person' becomes 'jerk' (I've seen this before).
'wearing' becomes 'in' (wear in (and 'in' is fashionable)).
'jerk'+'in'='JERKIN'
(Other definitions for jerkin that I've seen before include "leather jacket" , "sleeveless garment" , "Close-fitting sleeveless jacket" , "sort of jacket" , "Type of coat or jacket" .)