Irascible friend of Mole's (5)
I believe the answer is:
ratty
'irascible' is the definition.
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for ratty that I've seen before include "Waspish" , "Get annoyed" , "character on the river bank" , "with pests" , "Short-tempered" .)