Tries pants on wrong, looking ugly (8)
I believe the answer is:
sinister
'ugly' is the definition.
('sinister' can be a synonym of 'ugly')
'tries pants on wrong' is the wordplay.
'pants' is an anagram indicator (UK informal term for 'nonsense' or 'rubbish').
'on' indicates putting letters inside (as in clothing \'on\' a person).
'wrong' becomes 'sin' (I've seen this before**).
'tries' anagrammed gives 'ister'.
'ister' placed around 'sin' is 'SINISTER'.
'looking' acts as a link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for sinister that I've seen before include "Suggestive of evil, threatening harm" , "Threatening - ominous" , "Very unpleasant" , "Disquieting" , "Suggestive of evil/harm" .)