頓とん馬ま

na-adjective, noun

idiot; fool; dope

A somewhat dated, mild insult for a slow-witted or clumsy person. Often used in a teasing or self-deprecating way rather than as a strong slur.

• また鍵かぎを忘わすれたの？とんまだなあ。

  You forgot your keys again? You're such a dope.

• 彼かれはとんまな失しっ敗ぱいばかりする。

  He keeps making stupid mistakes.