昼行灯ひるあんどん

noun

dimwit; blockhead; person who is useless despite being present

Derogatory idiom literally meaning 'a lantern at noon'—someone who is as useless as a lantern in broad daylight, often implying inattentiveness or lack of common sense.

• あいつは昼行灯ひるあんどんで、何なにを頼たのんでもまともにできない。

  That guy is a dimwit; no matter what you ask him to do, he can't do it properly.

• 会かい議ぎ中ちゅうずっとぼんやりしていて、まるで昼行灯ひるあんどんだ。

  He was spacing out the whole meeting—he's like a lantern at noon.