Deliberate mistake: As Luanne is putting the dirt into Bobby's fruit pie you can see she rips open a large part of the packet. Yet in the next scene when Bobby is about to eat the pie there is no sign of where Luanne ripped the packet. Its likely this was deliberate as the joke in the scene was Bobby and Luanne's constant attempts to get back at each other, if they had left the large hole its likely Bobby would have not fallen for Luanne's prank.
Continuity mistake: During the scene where Peggy and Hank are enjoying a spa, Hank fills up the champagne glasses with beer. He stops pouring a bit before the top of the glasses and there is very little foam on the top. In the very next shot both their glasses have foam overflowing from it.
Continuity mistake: As Bobby visits Connie and is at her window he lays his hands on the window sill. The next shot they are back by his side and they keep alternating back and forth even though he never moves them between shots. At the end of the scene Connie shuts the window smoothly even though his fingers were still there in the shot before.