flab·ber·gast (flāb'ər-gāst') tr.v.
flab·ber·gast·ed, flab·ber·gast·ing, flab·ber·gasts To cause to be overcome with astonishment; astound. See Synonyms at surprise.
1772, mentioned (with bored) in a magazine article as a new vogue word, perhaps from some dialect (in 1823 it was noted as a Sussex word), likely an arbitrary formation from flabby or flapper and aghast.