It's a silly, silly thing, having to do with a right-wing television person's reaction to this picture of the Obamas:
Here's where the "terrorist fist jab" enters the game:
Teasing a segment on the "gesture everyone seems to interpret differently," Fox News' E.D. Hill said: "A fist bump? A pound? A terrorist fist jab? ... We'll show you some interesting body communication and find out what it really says." In the ensuing discussion with a "body language expert," Hill referred to the "Michelle and Barack Obama fist bump or fist pound," but at no point did she explain her earlier reference to "a terrorist fist jab."
See how the memes are being forwarded? In any case, that gesture, whatever it might be, has been used by George The Elder (from Phillybits via Eschaton):
Much ado about nothing, but also a way to forward that idea of Obama as a Manchurian candidate. In any case, anyone who has done boxing might point out that those are not jabs.