This is a commonly used phrase to represent when a person is somewhat surprised. Or at times people say it just because it is one of the most commonly represented phrases in our world today.
"Ass yo, my car was stolen, ass." "ASS YO." "Ass yo, I'm out."
" Luke likes it in the butt from gay latinos? Ass yo, doesn't surprise me."
nigga: yo son, you scuffed ma tims, imma pop a cap in yo ass
white man: ????
translator: he says because you have accidentallystepped on his costly Timberland footwear and caused small particles of debris to reside on said footwear, he will discharge a firearm into your body with the intent to cause grievous bodily harm