Aggravated, son donned trousers (5)
I believe the answer is:
worse
'aggravated' is the definition.
(I've seen this in another clue)
'son donned trousers' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'donned' becomes 'wore' ('wear' can be a synonym of 'don').
'trousers' means one lot of letters goes inside another (trouser can mean to steal or take).
's' going into 'wore' is 'WORSE'.
(Other definitions for worse that I've seen before include "Less satisfactory" , "Less favourable" , "Of poorer quality" , "less moral?" , "More serious" .)