Jane Schoenbrun ’s Teenage Sex And Death At Camp Miasma got one of the first extended standing ovations of this year’s Cannes Film Festival. Screening at the 1,068-seat Debussy Theatre on Wednesday night to open the festival’s Un Certain Regard section, the psychedelic tribute to the slasher-horror cycle of the early ’80s had the audience clapping for nine minutes (yes, it was that long), some of which occurred as star Hannah Einbinder thanked the cast and crew over a three-minute stretch. “Ok, what should we do now?” said Einbinder before launching into a generous list of thank-yous. The campy, blood squirting comedy follows a queer filmmaker (played by Einbinder) who in making a slasher franchise sequel becomes obsessed with casting the original film’s “final girl” ( Gillian Anderson ). Psychological and sexual chaos ensues.…