Oppressor’s extremely touchy diatribe (6)
I believe the answer is:
tyrant
'oppressor's' is the definition.
(I've seen this before)
'extremely touchy diatribe' is the wordplay.
'extremely' suggests removing the centre.
'diatribe' becomes 'rant' (I've seen this in other clues).
'touchy' with its middle removed is 'ty'.
'ty'+'rant'='TYRANT'
(Other definitions for tyrant that I've seen before include "Cruel and oppressive dictator" , "Oppressor" , "Harsh and absolute ruler" , "Despotic ruler" , "big bully" .)