Smirking, about to irritate (3)
I believe the answer is:
irk
'irritate' is the definition.
(to irk is to irritate)
'smirking about' is the wordplay.
'about' says the answer is hidden in the clue (the clue goes around or about the answer).
'IRK' is hidden in the letters of '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" .)