It's a classic sign of deception. Inappropriate laughter can signify that the person can't help but laugh at the idea that he or she is getting away with something.
Today, I was thinking about Hillary's “What, at this point, does it matter?”.
She got away with it. That ship sailed, it was down the road. Suddenly, there was a bunch of Congressworms axing snide questions.
Hillary was saying: "Trey. I got away with it. The Media will cover me with artillery barrage after artillery barrage. So, what, at this point, does it matter, Gowdy, you sniveling worm?"