Annoyed when infested with rodents? (5)
I believe the answer is:
ratty
'annoyed' is the definition.
(thesaurus)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for ratty that I've seen before include "character on the river bank" , "Irritable (informal)" , "Irritable, peevish" , "describing vermin" , "Bad-tempered, irritable as a rodent" .)