Psycho Beach Party (2000) on Netflix

Spoof of 1960's Beach Party/Gidget surfing movies mixed with slasher horror films stars Lauren Ambrose as Florence Forrest, a not-so-innocent girl in 1960's Malibu who becomes "Chicklet" the first girl surfer at Malibu Beach, only Florence suffers from dissociative identity disorder and occasionally her alter ego Ann Bowman, a sexually aggressive, foul-speaking girl, comes out in which during that time several beach goers are found murdered. The suspects include Chicklet herself, surfer Kanaka, B-horror film actress Bettina Barnes, exchange student Lars, and even Chicklet's own mother.