This word is used to describe children who "Just Aint Right"
Synonyms: POPP, stupid, dumb, naughty, never going to fit in types, not mainstream, messed up, etc, etc, and so forth.
they have little or no potential to be normal until they get the right treatment/therapy.
Hose: No he doesnt, Johnny is a JAR!
Alex: This boy needs to go to the institution
John: Yeah, there is nothing we can do about it. He is a JAR.
It means to be funny, silly or fun to be around.
Your such a 'jar'.
He's / She's such a jar to be around.
We jar'd out all night.
Your 'jarring' me out! (Meaning to be very funny or silly!)