sour grapes
US /ˈsaʊər ɡreɪps/
UK /ˈsaʊər ɡreɪps/
1.
an attitude in which someone pretends to dislike something because they cannot have it or achieve it
:
•
Her criticism of his new car was just sour grapes because she couldn't afford one herself.
•
He said he didn't want the promotion anyway, but I think it's just sour grapes.