Writhing in agony, holding front of nose, becoming tiresome (8)
I believe the answer is:
annoying
'tiresome' is the definition.
(I've seen this before)
'writhing in agony holding front of nose' is the wordplay.
'writhing' is an anagram indicator.
'holding' indicates putting letters inside.
'front of' suggests taking the first letters.
The initial letter of 'nose' is 'n'.
'in'+'agony'='inagony'
'inagony' anagrammed gives 'anoying'.
'anoying' placed around 'n' is 'ANNOYING'.
'becoming' acts as a link.
(Other definitions for annoying that I've seen before include "tiresome" , "Irking" , "It's galling" , "Disturbing, irritating" , "Vexatious" .)