Girl men upset is mischief-maker (7)
I believe the answer is:
gremlin
'is mischief-maker' is the definition.
(magical creature)
'girl men upset' is the wordplay.
'upset' indicates an anagram.
'girl'+'men'='girlmen'
'girlmen' is an anagram of 'GREMLIN'.
(Other definitions for gremlin that I've seen before include "Impish troublemaker" , "One sabotages" , "Pixie" , "Bug (in engine)" , "Cause of unexpected mechanical problem" .)