The reason that skit was humourous was because they were eating at a place dedicated to the sale of pizza. Therefore a man who was currently out with his friends wanted to make a joke asking for a cheeseburger. An item that isn’t pizza that he expected them not to have. This leads to a moment of laugh amongst his friends before it is shattered by their server saying that they do have pizza. The man is then shocked the dramatic face he makes is dramatized by a thud sound effect. The comedy coming from the drastic switch in tone.