顔かおに泥どろを塗ぬる

expression, godan verb (-ru)

bring disgrace on; put to shame; fling mud at

Idiomatic expression meaning to cause someone to lose face or be publicly humiliated. The image is of smearing mud on someone's face, i.e., dirtying their reputation.

• 彼かれの不ふ正せいが家か族ぞくの顔かおに泥どろを塗ぬった。

  His misconduct brought disgrace on his family.

• そんなことをしたら、先せん生せいの顔かおに泥どろを塗ぬることになるよ。

  If you do that, you'll put your teacher to shame.