Same as 'duh'. As in:
Boy says to girl: I am a boy
Girl says: Abuden. Gosh. Boys are idiots.
The short form of "Ah, but then?" to indicate, "What else did you expect?" or "Wasn't that obvious?"
A: I told her I would keep her cat while she went on vacation, but didn't realise I would have to feed the cat.
B: Abuden? Did you expect the cat to go look for food on its own?