Blabbergob is made up of two words blabber and gob.
'Blabber' meaning talk volubly, persistently, and usually inconsequentially (courtesy: answers.com)
".....Gob is the northern word for mouth.I used to live in Liverpool for many years and you'd say to people "ah, shut yer gob", you know, and it simply means, mouth.
So, to be 'gobsmacked' is to be struck dumb as if by a smack in the face....."
(Lesson 23,Gobsmacked from BBC Learning English – Keep your English up to date )
example2: I couldnt catch a wink of sleep in the bus, there was this blabbergob sitting next to me.