Rotten worker, curt (7)
I believe the answer is:
offhand
'curt' is the definition.
(both can mean brusque or rude)
'rotten worker' is the wordplay.
'rotten' becomes 'off' (rotten food is 'off').
'worker' becomes 'hand' (hand is a kind of worker).
'off'+'hand'='OFFHAND'
(Other definitions for offhand that I've seen before include "Cavalier" , "Ad lib" , "Casual; unconcerned" , "Nonchalant" , "with a careless manner" .)