No sex — am a government agent rejecting scandal (10)
I believe the answer is:
defamation
'scandal' is the definition.
(thesaurus)
'no sex am a government agent rejecting' is the wordplay.
'sex' becomes 'it' (a common euphemism).
'government agent' becomes 'fed' (I've seen this in another clue).
'rejecting' shows that the letters should be reversed in order (I've seen 'rejected' mean this).
'no'+'it'+'am'+'a'+'fed'='noitamafed'
'noitamafed' written backwards gives 'DEFAMATION'.
(Another definition for defamation that I've seen is " Assassination of character".)