Succeed with sex? Don’t be daft! (4,3,2)
I believe the answer is:
come off it
'don't be daft' is the definition.
I can't tell whether this defines the answer.
'succeed with sex?' is the wordplay.
'succeed' becomes 'comeoff' (I've seen this before).
'with' is a charade indicator (letters next to each other).
'sex?' becomes 'it' (a common euphemism).
'comeoff'+'it'='COME OFF IT!'
Can you help me to learn more?
(Other definitions for come off it that I've seen before include "Stop messing about!" , "Don't talk rubbish" , "Stop being so stupid!" , "People climbing dangerous structure may be told to" , "stop fooling" .)