大だいの大人おとな

expression, noun

grown-up; full-fledged adult; sensible adult

Used to emphasize that someone is a mature adult, often in contexts where childish or irresponsible behavior is surprising or inappropriate. Can refer to either gender.

• 大だいの大人おとながそんなことで泣なくなんて、みっともない。

  It's shameful for a grown adult to cry over something like that.

• 大だいの大人おとなが道みちに迷まよって、子こどもに道みちを聞きいた。

  A full-grown adult got lost and asked a child for directions.