Scoundrel's naughty urge (3,3)
I believe the answer is:
bad egg
'scoundrel's' is the definition.
(I've seen this in another clue)
'naughty urge' is the wordplay.
'naughty' becomes 'bad' (similar in meaning).
'urge' becomes 'egg' (as in egging someone on).
'bad'+'egg'='BAD EGG'
(Other definitions for bad egg that I've seen before include "Dishonest person like addled ovoid" , "A real stinker?" , "Rotter - something rotten!" , "Untrustworthy type (smelling rotten?)" , "Not a very good person, a rotten ovum" .)