負け犬の遠吠え
Meanings
1
backbiting of a coward; grumblings of a loser
Idiomatic expression describing someone who, after losing or retreating, complains or criticizes from a safe distance. The literal image is 'the distant bark of a defeated dog'.
His backbiting is nothing but the grumblings of a loser.
There's no need to listen to the coward's distant barking.