flabbergasted, astounded, shocked; also written gob-smacked
from gob 'mouth' + smacked 'clapping hand over in surprise'
by 1990, U.K. slang, from gob "mouth" + past participle of smack.
Extremely surprised: gobsmacked at the nomination
[1980s+; fr gob,''mouth,''and smacked, ''hit, struck,'' the theatrical gesture of clapping a hand over the mouth as a gesture of extreme surprise]