Bad-tempered person's so stuck up (4)
I believe the answer is:
ogre
'bad-tempered person's' is the definition.
(I've seen this before)
'so stuck up' is the wordplay.
'so' becomes 'ergo' (synonyms).
'stuck up' is a reversal indicator.
'ergo' back-to-front is 'OGRE'.
(Other definitions for ogre that I've seen before include "Wicked giant" , "Jack's giant perhaps" , "Terrifying person" , "Man-eating giant of folklore" , "Terrifying monster" .)