Mocking expression (5)
I believe the answer is:
sneer
'mocking expression' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sneer that I've seen before include "Show contempt with scornful expression or words" , "Taunt" , "Contemptuous gesture" , "Contemptuous expression" , "Contemptuous or mocking smile" .)