Is the sacrastic version of the word "yeah".
Person 1: "I'm am so going to beat you!"
Person 2: "Jyeah!"
A super-cool version of yeah, used in super-cool situations. Also, an exclamation when ultimate orgasmic happiness is reached.
Roddy: Dude, I just totally boned the captain of the cheerleading squad!!
Josh: Aww jyeah!