Coming from Denis such remarks aren't nice (5)
I believe the answer is:
snide
'such remarks aren't nice' is the definition.
(I've seen this before)
'coming from denis' is the wordplay.
'coming from' indicates an anagram.
'denis' with letters rearranged gives 'SNIDE'.
(Other definitions for snide that I've seen before include "Sarcastic" , "Derogatory, sneering" , "Derogatory in an insinuating way" , "Mean, base" , "Sneering, supercilious" .)