Much to Peggy's dismay, Hank's sexist father drops by to celebrate Bobby's birthday.
Leafing through the mail, Hank notices that Bobby's birthday invitation to Grandpa Cotton was returned. He then realizes that Bobby wrote "Hell, USA" as the mailing address. Bobby explains that Peggy told him Cotton was the devil. The boy then recites a list of things he dislikes about his grandfather: his big plastic teeth, his incessant screaming, and his lack of shins. Hank explains that Cotton lost his shins "defending Texas in World War II." Bobby telephones his grandfather and invites him to the celebration. The day of the party, a Cadillac pulls into the driveway, a horse trailer in tow. The trailer's ramp is kicked open from the inside, and Cotton rides the horse into the Hill's backyard. Eyes shining, and assuming the animal is a gift, Bobby tells his grandfather how much he loves the horse. But Cotton explains the horse is being rented for only a few hours. Later, he gives Bobby his real present: a 20gauge shotgun. Outraged, Peggy snatches the weapon from his hands. When Bobby is unable to break open his birthday pinata, Cotton blows it apart with the gun. Peggy asks Cotton to leave the house after he smashes her good dishes. But when the old man attempts to start his car, the engine fails to turn over. Luanne diagnoses the problem as a solenoid plunger. Peggy tells Hank she wants the "illtempered, foulmouthed old man" out of her house. But Hank tells his father he is welcome to stay.
Cotton takes Bobby to a local bar, where he harasses waitresses with sexist remarks. Meanwhile, Peggy finds the missing solenoid plunger hidden in a pair of Cotton's pants. She tells Hank that his father deliberately removed the part so he could stay at the house. Events turn even uglier when Cotton's sexist remarks begin influencing Bobby's behavior. Bobby tells his mother to get his dinner and punctuates his point by slapping her on the rearend.
Hank admonishes Bobby for hitting his mother. He then attempts to tell his father why his behavior around Bobby is inappropriate. But before Hank has a chance to speak, his father reiterates the tale of how he lost his shins in World War II. After listening in awe to the patriotic story, Hank decides to drop the idea entirely. But when Bobby is sent home from school for starting a "sexist riot," Hank decides his father has gone too far. He tells Cotton he won't let his son grow up to be a "woman-hating old fool" and orders him out of the house.