Mocking after adult's wrong (4)
I believe the answer is:
awry
'wrong' is the definition.
(synonyms)
'mocking after adult's' is the wordplay.
'mocking' becomes 'wry' (I've seen this in another clue).
'after' means one lot of letters go next to another.
'adult' becomes 'a' (abbreviation).
'wry' after 'a' is 'AWRY'.
(Other definitions for awry that I've seen before include "Askance, askew" , "Crooked; amiss" , "'Askew, twisted (4)'" , "Crooked, twisted to one side" , "(Gone) askew" .)