Spike — insult (4)
I believe the answer is:
barb
This clue is a double definition.
'spike' is the first definition.
(I've seen this before)
'insult' is the second definition.
(I've seen this in another clue)
(Other definitions for barb that I've seen before include "Aggressive remark intended to have a telling effect" , "Backward projecting point of an arrowhead" , "Arrow projection" , "Insult" , "Woundingly pointed remark" .)