what does it mean anyways?
What dattebayo/Dattebane/Shannaro mean is really all about context.
It is a corruption of joudan ja nai yo (冗談じゃないよ) which is a colloquial term literally meaning "this is not a joke" and can be loosely interpreted as: "stop kidding around", "don't fool yourself", "stop messing around", "you got to be kidding me", "yeah, right"---So there are a lot of different meanings that could be applied to it, but the feeling is the same.
She's starting to get pissed and you should high tail it out of there
Dattebayo is a bit different in the fact that he tags it onto a verb steam like uh..Wakka(ttebayo!) Meaning "I get it already". So its like if you were to go around saying " That kitten is jumping-nyerk." its just a sound that he adds to his sentences.