Stupid, foolish, or idiotic (used as a na-adjective to describe someone or something as foolish).
そんな間抜けなミスは誰にでもあるよ。
Everyone makes such a foolish mistake sometimes.
彼は間抜けな顔をして驚いていた。
He looked surprised with a silly expression on his face.
間抜けな返事をしてしまって恥ずかしかった。
I gave a foolish answer and felt embarrassed.
A fool; an idiot; a blockhead (used as a noun for a foolish person).
彼はいつも間抜けでみんなにからかわれている。
He's always being foolish and everyone teases him.
あんな間抜けに仕事は任せられないよ。
You can't entrust work to such a fool.