Favourite clue reused about an irritable mood (9)
I believe the answer is:
petulance
'irritable mood' is the definition.
(I know that irritable mood can be written as petulance)
'favourite clue reused about an' is the wordplay.
'favourite' becomes 'pet' (synonyms).
'reused' indicates an anagram.
'about' is an insertion indicator.
'clue' is an anagram of 'ulce'.
'ulce' going around 'an' is 'ulance'.
'pet'+'ulance'='PETULANCE'
(Other definitions for petulance that I've seen before include "ill humour" , "Childish bad-temper" , "Peevish irritation" , "Childish sulkiness" , "Bad temper, sulkiness" .)