Venom (1966)

Per, a hedonistic young man who simply shows up one day on a speedboat outside a well-to-do family's summer house. Befriending family's daughter, Susanne, the coolly amoral Per does everything he can to shake their complacency, just for the hell of it. He delights in stirring up trouble with his video camera, screening filmed private intimate moments to the mother of the daughter who is prominently featured on the video.