It means "off the wall," "out of this world," "shut up! your kidding," and many other related things. It is used to describe something that was totally amazing, you cant say anything at all, and you cant describe it. You only have to say it, and everyone will know what you mean.
It originated in the Kansas City area. It is used quite frequently by the teenagers there
Wife: Hey, Honey! I just won the lottery! We gonna BE RICH!
Husband: That shit is bahdoh!!! :D