Dress I treat badly (6)
I believe the answer is:
attire
'dress' is the definition.
(I know that dress is a more specific form of attire)
'i treat badly' is the wordplay.
'badly' is an anagram indicator (letters in the wrong order).
'i'+'treat'='itreat'
'itreat' is an anagram of 'ATTIRE'.
(Other definitions for attire that I've seen before include "Wear" , "12" , "Prepare" , "Special clothing" , "Garments" .)