Upset when I complain (5)
I believe the answer is:
whine
'complain' is the definition.
(I know that whine is a more specific form of the action complain)
'upset when i' is the wordplay.
'upset' is an anagram indicator.
'when'+'i'='wheni'
'wheni' anagrammed gives 'WHINE'.
(Other definitions for whine that I've seen before include "beef?" , "Petulant complaint" , "carp" , "Querulous complaining" , "Grumble" .)