Definitions by Yogi!!

gobsmack 

To be completely dumbfounded or shocked. That I know of, its origins are Irish.

I have know idea what a "gob" is or why it is common practice to smack somebody with one when they are shocked.

It seems like a rude thing to do, though.

"Well, I'll be gobsmacked!" exclaimed the taxi driver, as he watched two sworn enemies hug.

gobsmack by Yogi!! April 18, 2005