Complaint isn't about Mel getting agitated (7)
I believe the answer is:
ailment
'complaint' is the definition.
(I know that complaint can be written as ailment)
'isn't about mel getting agitated' is the wordplay.
'isn't' becomes 'aint' (non-standard version of 'isn't').
'about' is an insertion indicator.
'getting agitated' indicates anagramming the letters.
'mel' with letters rearranged gives 'lme'.
'aint' enclosing 'lme' is 'AILMENT'.
(Other definitions for ailment that I've seen before include "Complaint, affliction" , "Tummy upset, for instance" , "Slight but persistent illness" , "Sickness" , "Physical disorder" .)