大おお真面目まじめ

na-adjective

deadly serious; deadly earnest

Emphasizes extreme seriousness, often with a nuance of being overly or comically earnest. Used for people, expressions, or attitudes.

• 彼かれは大おお真面目まじめな顔かおで冗じょう談だんを言いった。

  He told a joke with a dead serious face.

• そんな大おお真面目まじめに考かんがえなくてもいいよ。

  You don't have to think about it so deadly seriously.