Nick run down on vacation (5,3)
I believe the answer is:
knock off
'nick' is the definition.
'run down on vacation' is the wordplay.
'run down' becomes 'knock' (both can mean to criticise or disparage**).
'on vacation' becomes 'off' (off can mean away on holiday).
'knock'+'off'='KNOCK-OFF'
(Other definitions for knock off that I've seen before include "call it a day" , "Stop work (informal)" , "finish work" , "Down tools" , "half-inch > pack in work" .)