De queixo caído = flabbergasted
Gina was flabbergasted when the doctor told her she was pregnant.

(Gina ficou de queixo caído quando o médico disse que ela estava grávida.)
When the children went to see the magician, they were flabbergasted when he made a rabbit disappear.
When the children went to see the magician, they were flabbergasted when he made a rabbit disappear.
(Quando as crianças foram ver o mágico, ficaram de queixo caído quando ele fez o coelho desaparecer.)
Everybody was flabbergasted when I announced I was going to the United States.
Everybody was flabbergasted when I announced I was going to the United States.
(Todo mundo ficou de queixo caído quando eu anunciei que iria para o Estados Unidos.)