Prone to pique (8)
I believe the answer is:
petulant
'prone to pique' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for petulant that I've seen before include "peevish impatience" , "Sullen in a peevish way" , "Pouting" , "Irritable, sullen" , "Fractious, pouty" .)