noun
memory like a sieve; in one ear and out the other
Idiomatic noun describing a person who quickly forgets what they hear, as if their ears are like a leaky basket. Often used self-deprecatingly or to tease someone.
彼は籠耳だから、大事なことはメモしておいたほうがいいよ。
He has a memory like a sieve, so you'd better write down important things.
ごめん、籠耳でさっきの話を忘れちゃった。
Sorry, I've got a memory like a sieve and already forgot what you just said.
Compound of 籠 (かご, 'basket') and 耳 (みみ, 'ear'), literally 'basket ear,' likening a forgetful ear to a basket that cannot hold water.