Denis, shiftily, being maliciously derogatory (5)
I believe the answer is:
snide
'maliciously derogatory' is the definition.
(I've seen this in another clue)
'denis shiftily' is the wordplay.
'shiftily' is an anagram indicator (I've seen this in other clues).
'denis' anagrammed gives 'SNIDE'.
'being' is the link.
(Other definitions for snide that I've seen before include "Delivering cuts" , "such remarks aren't nice" , "Sneering in a sly way - dines out on it" , "Indirectly mocking" , "Derogatory, showing malice" .)