with one's mouth open
Por que está aí parado de boca aberta idiota?
Why are you standing there with your mouth open, idiot?
— Брат 2 (2000)
Tom disse ao filho para não comer de boca aberta.
Tom told his son not to eat with his mouth open.
E fica todo mundo de boca aberta!
And everyone is left speechless!
— Stalker (1979)