Messed up final agonising (7)
I believe the answer is:
painful
'agonising' is the definition.
(I've seen this before)
'messed up final' is the wordplay.
'messed' is an anagram indicator (letters get messed up).
'up'+'final'='upfinal'
'upfinal' is an anagram of 'PAINFUL'.
(Other definitions for painful that I've seen before include "Causing physical discomfort" , "Sore" , "Wretched" , "Causing trouble or difficulty - it hurts" , "Hurting" .)