Overly serious; extremely earnest to the point of being inflexible or lacking a sense of humor.
彼は生真面目で、飲み会では冗談が通じないことが多い。
He's overly serious, and jokes often don't get through to him at drinking parties.
仕事では生真面目な態度が評価される場合もある。
An overly earnest attitude can sometimes be valued at work.
そんなに生真面目に考えなくてもいいよ、リラックスして。
You don't have to take it so seriously — relax.
子どもの頃から生真面目で、約束は必ず守る性格だ。
He has been very earnest since childhood and always keeps his promises.