From das wiki: "The film tells the story of 21-year-old Benjamin Braddock (Dustin Hoffman), a recent college graduate with no well-defined aim in life, who is seduced by an older woman, Mrs. Robinson (Anne Bancroft), and then falls in love with her daughter Elaine (Katharine Ross)."
Mother and daughter? The film was a mild hit with wild imagination, teenaged boys, but it was really more cynical soap opera with a muddled ending than titillation.
The 'plastics' reference is to a family friend who bends the ear of the recent, aimless graduate in order to impart unsolicited career advice. Thankfully, it was an analog age, so the abuse of 'Learn to Code' was still 30 years out.
I thought this post was about plastics?
"On February 5, 1909, New Yorker Leo Baekeland presented his invention of Bakelite, the first synthetic plastic, to the American Chemical Society."
Happy now? Wait. There's more: "Being moldable and heat resistant, Bakelite found immediate use in electrical fixtures and telephones as well as toys, auto parts and many household objects.
Later inventions of other plastic products gave us the incredible array of plastic products we know of today, from toothbrushes and clothing fibers to food preservation and sextoys!"
Search engine that last one. I ain't going there.