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".
Possible usage: YA FACE! OH-MY-GOD, YA FACE! Oh hey by the way, YA FACE!