Target of ridicule in genuine denial (8)
I believe the answer is:
rebuttal
'denial' is the definition.
(I've seen this before)
'target of ridicule in genuine' is the wordplay.
'target of ridicule' becomes 'butt' (as in the butt of a joke).
'in' means one lot of letters goes inside another.
'genuine' becomes 'real' (similar in meaning).
'butt' put inside 'real' is 'REBUTTAL'.
(Other definitions for rebuttal that I've seen before include "resistance to attack" , "Counter-statement" , "statement delivered to counter" , "Refuting argument" , "contrary argument" .)