A babbling, foolish person
This is my favorite word from Mark Twain's short story "The Man that Corrupted Hadleyburg."
The Tanner: "And so, if the Chair will examine the test-remark in the sack, we shall know which of these two frauds--[The Chair. "Order!"]--which of these two adventurers--[The Chair. "Order! order!"]--which of these two gentlemen--[laughter and applause]--is entitled to wear the belt as being the first dishonest blatherskite ever bred in this town--which he has dishonoured, and which will be a sultry place for him from now out!"
Did you ever watch Ducktales? The bean counter Fenton Crackshell turned into the superhero Gizmo Duck by yelling "blabbering blatherskite!" That used to be my favorite show when i was little :)