A pain in the neck about police officer (5)
I believe the answer is:
garda
'police officer' is the definition.
(member of the Irish police)
'a pain in the neck about' is the wordplay.
'pain in the neck' becomes 'drag' (both can mean something annoying).
'about' says the letters should be written in reverse.
'a'+'drag'='adrag'
'adrag' written backwards gives 'GARDA'.
(Other definitions for garda that I've seen before include "One of our police - what a drag" , "Irish state police force" , "Irish police officer" , "Member of the police" , "Italian lake - Irish policeman" .)