Charlie Brown expletive (4)
I believe the answer is:
rats
'charlie brown expletive' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rats that I've seen before include "Rodent pests" , "deserters" , "Snoopy's imprecation - vermin" , "Curse" , "Treacherous rodents" .)