Bother celebrity in retreat (4)
I believe the answer is:
rats
'bother' is the definition.
(exclamation of frustration)
'celebrity in retreat' is the wordplay.
'celebrity' becomes 'star' (I've seen this before).
'in retreat' says the letters should be written backwards.
'star' reversed gives 'RATS'.
(Other definitions for rats that I've seen before include "Treacherous rodents" , "Damn" , "Rodent pests" , "Heels" , "Mild oath - sewer residents" .)