Deserter extremely touchy and bad-tempered (5)
I believe the answer is:
ratty
'bad-tempered' is the definition.
(I've seen this before)
'deserter extremely touchy' is the wordplay.
'deserter' becomes 'rat' (both can mean a traitor).
'extremely' suggests removing the centre (only the extremes of the word are used).
'touchy' with its centre removed is 'ty'.
'rat'+'ty'='RATTY'
'and' is the link.
(Other definitions for ratty that I've seen before include "Irritable (informal)" , "Bad-tempered, irritable as a rodent" , "One messing about in a boat" , "Character created by Kenneth Grahame" , "Moley's friend" .)