Smirking, about to irritate (3)
I believe the answer is:
irk
'irritate' is the definition.
(thesaurus)
'smirking about' is the wordplay.
'about' indicates the answer is hidden within the clue.
'IRK' can be found hidden inside 'smirking'.
'to' acts as a link.
(Other definitions for irk that I've seen before include "Gall" , "Annoy in quirky way" , "English river" , "Wind up" , "Severely annoy" .)