A disparaging term for a foolish person; fool/idiot (colloquial, often insulting).
そんなことを言うなんて、馬鹿者だよ。
Saying something like that — you're a fool.
彼は試験を忘れて、みんなに馬鹿者扱いされた。
He forgot the exam and everyone treated him like an idiot.
馬鹿者！危ないから勝手に動くな。
Idiot! Don't move on your own — it's dangerous.