verb

1. To overwhelm with bewilderment; to amaze, confound, or stun, especially in a ludicrous manner.

   “He was flabbergasted to find that his work had been done for him before he began.”

Synonyms: flabbergaster

adjective

1. Appalled, annoyed, exhausted or disgusted.

   “He was flabbergasted at how much weight he had gained.”

2. Damned.