Sore loser's attitude (4,6)
I believe the answer is:
sour grapes
'sore loser's attitude' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sour grapes that I've seen before include "Disparagement of something one wants but cannot attain" , "Disdain that covers disappointment" , "with a bitter aftertaste?" , "Feigned dislike" , "Bitterness" .)