Conversation Piece (1977) on Netflix

A 60-ish American art collector and former scientist (the Professor) lives beautifully and alone in Rome but his life is radically disrupted when the wife of a rightist industralist, the Marchesa Brumonti, her young lover, Konrad, teen-aged daughter, Lietta and her daughter's boyfriend, Stefano lease the upper apartment of the luxurious palazzo he has inherited from his Italian mother. Against his judgment, the Professor becomes involved in the affairs of these distasteful strangers who begin to hold a strange fascination for him. The Marchesa is beautifully dressed and coiffed, but her behavior is loud and vulgar. Konrad describes a leftist activist past in contrast to his degenerate present which may involve drug dealing. Lietta and Stefano are sexually precocious, and they are all very stylish. They encroach more and more upon the Professor's privacy and thoughts until they become like the family he wants to disown but can't because they are his kin. The Professor's memories of his mother and wife intervene and his art collection and bedside reading hold clues to the violent psycho-drama that ensues. The sumptuous interiors are ravishing.