"Father Knows Worst" is the eighteenth episode of season 20.
When Homer believes that Bart's under achievements and Lisa's unpopularity will jeopardize their future, he tries "helicopter parenting" - that is, he hovers over them constantly; meanwhile, Marge is too busy relaxing in the mysterious new basement sauna she just happened to find in the basement to care.
While out at a carnival on the South-Side Sea Port, Homer accidentally swallows a flaming stick (thinking it was a kebab) and burns his tongue (which was worsened from Bart pranking Homer by tricking him into ingesting lighter fluid) to the point where his old tastes buds have been destroyed revealing new sensitive taste buds, making him a "super-taster". This makes the flavor of any food he eats magnify to such a degree that it becomes inedible, he is no longer able to eat anything with even the slightest bit of taste, leaving only cafeteria food Lisa brings home because it has absolutely no flavor whatsoever. He chooses to come to Springfield Elementary to eat during lunch, embarrassing Bart in the process. He sits at a lunch table and meets a mother who's a "helicopter parent", who comes to school with her boy, Noah, and makes sure he does well. Homer observes how stupid Bart is and how unpopular Lisa is, so he plans to help them out. He and Bart compete in the Plywood sculpture assignment, but the Washington Monument choice is too pathetic by Skinner's standards, so Homer goes for the hardest one of all, the "Westminster Abbey" model. He also helps Lisa get into the in-crowd with the help of a popularity book and a cell phone cover decorating party.
Homer sees that Bart will no doubt screw the project up and he offers to do it himself. He falls asleep and the ghosts that haunt the building advise him to let Bart do it, as he will not gain knowledge unless he does something. However, Homer moves in his sleep and demolishes his model. At the contest ceremony, Bart's model wins for looking like the only one who did not had help from their parents. Bart declines and reveals Homer did it and tells his father to not mess with his lifetime. Lisa also tells him this, as she does not like being cool, as it is hard work.
Meanwhile, Marge discovers a sauna in their basement and loves it, keeping it to herself. She becomes so relaxed that she is dazed when Homer tells her the kids' problems. Later, after Homer fails as a parent, Marge reveals it to him and they end up kissing nude (covered by the heat steam).