Opposite or contrary to what is expected, completely disordered or disarranged, or that which is done incompetently. A euphemistic rearranging of "ass-backwards" (meaning the same) to emphasize the disorder at play. That's the last time I let you fix the electrical work by yourself. You've wired it all bass-ackwards! I must not be completely awake yet, I just put my pants on bass-ackwards!