Clobber that's horrible, one criticising clothing (9)
I believe the answer is:
slaughter
'clobber' is the definition.
'that's horrible one criticising clothing' is the wordplay.
'that's horrible' becomes 'ugh' (expression of disgust).
'one criticising' becomes 'slater' ('slate' can mean to severely criticise).
'clothing' is an insertion indicator.
'ugh' placed within 'slater' is 'SLAUGHTER'.
(Other definitions for slaughter that I've seen before include "Killing (of farm animals)" , "Wholesale killing" , "Glare thus to cause bloodthirsty killing" , "Kill cruelly" , "Murder" .)