Twitch is part of villain's complaint (9)
I believe the answer is:
criticism
'complaint' is the definition.
'twitch is part of villain's' is the wordplay.
'twitch' becomes 'tic' (tic is a kind of twitch).
'part of' means one lot of letters goes inside another (part of the inside).
'villain' becomes 'crim' (short for criminal).
'tic'+'is'='ticis'
'ticis' put into 'crim' is 'CRITICISM'.
(Other definitions for criticism that I've seen before include "Examination and judgment of something" , "Evaluation or fault-finding" , "Finding fault" , "Disapproval; review" , "Evaluation of a work of literature" .)