Laughing on the bench is a touchy subject because the players are human and the scoreline was so ridiculous I think human nature is to laugh.
However part of the Alexis mythology is that he hates losing and never gives up and blah blah blah blah. He was awful tonight, coughed up the ball near his own box leading to a goal, totally quit on that play btw and then had a chuckle on the bench. It wasn't cool of him to do that and it's pretty clear that he'll be gone in the summer.
He's a great player but I don't know that he'll find the star role he's looking for somewhere else. Maybe at Juventus, but I doubt Dybala is going to play second fiddle to Alexis.