thick as a brick

Adjective

not-comparable

(simile) Very stupid; slow to learn or understand.

Japanese Meaning

非常に愚かである / 学習や理解が非常に遅い

He was thick as a brick when he tried to pay with expired coupons at the store.

彼は店で期限切れのクーポンで支払おうとしたとき、とても頭が悪かった。

Sense（1）

(simile) Very stupid; slow to learn or understand.