A return of the infamous middle finger along the jaw (the F*** YOU gesture).
I don't expect to see that. Obama's handlers must know that would be seen as juvenile in a live televised debate.
But, yes, I know... that hasn't stopped him before.
I will wager one donut that the finger will be flying.
BTW, the picture I cited in the text of Obama firing the finger off, IS in a debate. McCain/Obama in 2008.