Here it is: "I have to say my flabber has never been so gasted." by blogger Sally
The word, of course, is Flabbergast and I had to find out more about it.
It turns up first in print in 1772, in an article on new words in the Annual Register. Presumably some unsung genius had put together flabber and aghast to make one word... The source of the first part is obscure. It might be linked to flabby, suggesting that somebody is so astonished that they shake like a jelly. It can’t be connected with flapper, in the sense of a person who fusses or panics, as some have suggested, as that sense only emerged at the end of the nineteenth century. But flabbergasted could have been an existing dialect word, as one early nineteenth-century writer claimed to have found it in Suffolk dialect and another — in the form flabrigast — in Perthshire. Further than this, nobody can go with any certainty.
*excerpted from World Wide Words.org, Michael Quinion
Flab`ber*gas*ta"tion\, n. The state of being flabbergasted.