Well, that argument lasted like two seconds, right? We want to know what's funny as much as you do. Who could they be gossiping about. Our little liars could be laughing at anyone, we don't judge them!
It's Caleb, but what is he not happy about? Well, let's be honest, no one in this image looks happy. It looks as if the liars know something incriminating about him, but as always, we'll have to tune in to see what is really going on. Looks can be deceiving in Rosewood.
Given that the official episode description says that Kenneth Dilaurentis gives the liars clues they need in order to find out the truth once and for all,it only seems natural that the liars would be a little under pressure to get to the Radley documents before they are destroyed.
You think the truth is this big shiny disco ball of purity then go ahead and try it. See what it gets you. Telling the truth to the wrong person at the wrong time is how I ended up where I did. Take it from me you're always better off with a really good lie.