J34, commonly used by gamers in the northeast originated in around the year 2004. Copious rap songs were debuting at the time who included the token background singer who simply yelled "yea! yea! cheah!! geeyaah!! geeyah!!" at every oppurtunity.
when using the word, it is often drawn out and used in a stonerish manner. often it is accompanied by a prefix, like "ohhh" or "shitttt".
it can be used as a replacement for the word "yea", or even as a verb.
Kid 1:"you want to go bang those nips over there"
Kid 2:"Ohhhhhhh ShitJ344444!"
kid 1:"this herb is great, j34 this shit"
kid 2:"oohhhh j333333444444"