It is a phrase that can be used when a person does not have the energy to respond with any other coherent answer. Also used when a quick witted comeback eludes your mind.
A term coined by Lewis Camacho (arguably the most charming and important non-intellectual of our time -beat that Chomsky-). A virulent phrase meant to envoke sadness in the recipient and display pure contempt for the recipient. It evolved from the latin "I laugh in Ya Face" which because of the actual laughing couldn't be fully understood hence HAAAHAHA "YA FACE".
this is commomly used when someone says something harsh to ya and you cant be arsed to say anything back so you just reply ya face is and there you are problem solved.