Opposites Attract: Night of the Locust (3) - S2-E15
Other mistake: The filming of the spycam at the dance doesn't make sense. Grandpa and Judy are roughly the same height. The spycam was placed in his shirt pocket. Yet, when he looks over at her, her head is right in the middle of the shot, when in reality it would have been much higher up, and likely out of frame.