Short for, "Just kidding, all the way". It is used by many of the same people who say things like, "See you later, alligator" and "Bye-bye butterfly". It is presumed that the kind of people who say these things suffered some sort of serious rhyme shortage as children.
"Hey, did you hear? Jerry just got hit by a car!"

"Oh my god, is he okay?"

"Haha, you fell for it! JK all the way!"
by Se@horse15 June 13, 2012
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