Evil doctor repeated unacceptable act (2-2)
I believe the answer is:
no-no
'unacceptable act' is the definition.
(I've seen this before)
'evil doctor repeated' is the wordplay.
'evil doctor' becomes 'No' (Dr No, James Bond villain).
'repeated' says to double the letters.
'no' duplicated is 'NO-NO'.
(Other definitions for no-no that I've seen before include "Non-starter" , "Unacceptable act" , "Impossibility" , "turn-off for some?" , "Something that must not be done (informal)" .)