JA! is a way of saying "In your face" without sounding lame as hell by saying "in your face"
"yeah thats not what your mom was thinking last night.....oh yeah....i went there....so JA!"
If someone has a "J" in the beginning of their name, or a "J" in your name, JA! is a noise you make instead of saying the person's name if you're in a class room or somewhere quiet. JA! is a sound.
JA! JA! (JA!ohn) (JA! oe) (andJA!rew)