na-adjective
foolish; stupid; ridiculous; absurd
Expresses that something or someone seems foolish, idiotic, or absurd. Often used in a self-deprecating or exasperated way.
こんな簡単な問題が解けないなんて、ばかみたい。
It's stupid that I can't solve such a simple problem.
彼
His excuse sounded ridiculous.
馬鹿 is a noun meaning 'fool' or 'idiot', while 馬鹿みたい is an adjectival noun meaning 'foolish' or 'ridiculous'.
馬鹿らしい is an i-adjective with a similar meaning, but 馬鹿みたい often carries a more subjective, impressionistic nuance ('seems foolish').
Derived from 馬鹿 (fool) + みたい (seems like). The exact origin of 馬鹿 is uncertain, with theories including a Sanskrit loanword or a Chinese story.