expression
completely worthless; utterly useless
A strong, derogatory set phrase meaning something or someone is of absolutely no use. The literal image is 'not even useful as shit.' Used in informal, often angry or dismissive speech.
あんな奴は糞の役にも立たぬ。
That guy is completely worthless.
この説明書、糞の役にも立たぬな。
This manual is utterly useless.
A fixed derogatory expression combining 糞 (くそ, 'shit') with the phrase 役に立たぬ ('not useful'). The literal meaning is 'not even useful as shit,' emphasizing total worthlessness.