Under the Carp Banner / Chikan waisetsu nozoki / 痴漢わいせつ覗き (1992) dir. Kazuhiro Sano

Kazuhiro Sana and his girlfriend Kanako Kishi decide to steal a car and go to visit her relatives at a country resort. The two are the epitome of westernized Japanese youth. They visit a hot tub resort in the off-season. Kishi's sister and her husband live there with their son, who has never matured past the day when he fell off the roof. He now spends all of his time waving a carp banner. The brother-in-law is impotent, and has decided that he is a water spirit, and speaks only in a made up language. His wife devotedly has learned this language. Our two heroes decide to show Tokyo to the carp boy, which proves to be a big mistake.