Slyly sarcastic
I believe the answer is:
snide
'slyly sarcastic' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for snide that I've seen before include "Derogatory, sneering" , "Maliciously derogatory" , "Unpleasantly mocking" , "Mean, base" , "Supercilious, malicious" .)