Despot with extremely tetchy tirade (6)
I believe the answer is:
tyrant
'despot' is the definition.
(I know that despot can be written as tyrant)
'with extremely tetchy tirade' is the wordplay.
'with' is a charade indicator (letters next to each other).
'extremely' means to remove the middle letters (only the extremes of the word are used).
'tirade' becomes 'rant' (both can mean an angry outburst).
'tetchy' with its centre removed is 'ty'.
'ty' put next to 'rant' is 'TYRANT'.
(Other definitions for tyrant that I've seen before include "Harsh and absolute ruler" , "Oppressive and cruel ruler" , "Despotic ruler" , "bully - with 17d" , "Person dictating" .)