遣やり損そこなう

godan verb (-u)

fail to do; mess up; botch

Used when someone attempts an action but fails or makes a mistake in the process. Often implies a blunder or a slip-up.

• 大だい事じなプレゼンをやり損そこなって、上じょう司しに怒おこられた。

  I messed up the important presentation and got scolded by my boss.

• 簡かん単たんな計けい算さんをやり損そこなうなんて、疲つかれているのかもしれない。

  Making a mistake on a simple calculation like that—maybe you're tired.