Bad-tempered friend of Mole (5)
I believe the answer is:
ratty
This clue is a double definition.
'bad-tempered' is the first definition.
(I've seen this before)
'friend of mole' is the second definition.
(I know this)
(Other definitions for ratty that I've seen before include "water vole, literally" , "One messing about in a boat" , "Short" , "Irritable (informal)" , "Character created by Kenneth Grahame" .)