the first usage i can remember was probably in the late 1980s on a popular chicago area underground bulletin board system BBS called Ripco, and more recently i have seen it in common usage on IRC.
it is usually used in particulary derogatory and demeaning sentences due perhaps to replacing the softer "z" ending with the harder "t", suggesting a more forceful jisming or perhaps the finality of that last drop of jit.
Of course this also suggests usages such as Jitting, jitts, has jitted, full of jitt etc.
Also, if one spits spit and then has a puddle of spittle, would one jitt jitt and then have a puddle of jittle?
She was so nice, she must have swallowed a two-litre of my jitt last night.
Me: and by jitt i mean compliment
You: oh holy jitt i was kinda worried there
You: and by jitt i mean chinese people
Me: wtf dude