A phrase used to emphasize you can't believe it; as in can't believe something just said, seen, heard, or otherwise experienced.
See phrase "I don't even know"
Cat: What up b*tches?
Dog1: (looking at dog2) Aw Hail Naw
Dog2: ?? Pppp... He ain't talking to me...
Dog1: Dog2! Dam! What up boy!!?
Dog2: (turning to see Dog1) Aw Hail Naw!!
Mah nukka! Ain't seen you in years!
Dog1: So you rollin' with that cat now?
Dog2: Aw Hail Naw (disbelieving what he just heard)
Dog1: (Discovering that his Dog food is gone) Aw Hail Naw! Who ate my Dog Chow!?