To rib (5)
I believe the answer is:
tease
'to rib' is the definition.
(I know that blackguard is a is a more specific form of the action of tease)
This is the entire clue.
(Other definitions for tease that I've seen before include "Pull leg of" , "Rib, wind up" , "Tantalize" , "Annoy good-naturedly" , "Josh" .)