Shabby chap, extremely grumpy (5)
I believe the answer is:
mangy
'shabby' is the definition.
(thesaurus)
'chap extremely grumpy' is the wordplay.
'chap' becomes 'man' (I've seen this before**).
'extremely' means to remove the middle letters.
'grumpy' with its centre removed is 'gy'.
'man'+'gy'='MANGY'
(Other definitions for mangy that I've seen before include "Having a skin disease" , "Scabby" , "Shabby - moth-eaten" .)