Cheesed off (12)
'cheesed off' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for irked that I've seen before include "Wound" , "Galled" , "Exasperated" , "Bugged" , "disgusted" .)
(Another definition for discontented that I've seen is " Restless and unhappy".)