The story behind it is that it's a mock storyboard that the writers did to relieve stress. Apparently, that specific one was passed around the office for quite a long time, and was several pages long. It started with Tommy trying to poison Angelica with Draino, but after a few pages it essentially turned into an extended graphic sex scene. Eventually, it got passed over to the Wild Thornberrys studio, where one of the guys working there reported it to the higher ups and that was the end of it.