In Cold Blood (1967)

Two years before Midnight Cowboy tackled male prostitution and mentioned blowjobs, but right in the middle of all the envelope-pushing of the 1960s, In Cold Blood (1967)'s dialogue between its two disreputable main characters is a great example of the progressive cinema of its time. Phrases like "I hate to think how much classy pussy that has cost me," and "he's a flaming faggot," and "just a quickie in the back seat," were definitely edgy for 1967, and foretold the cynical, hardcore pursuit of reality that defined 70s cinema. Oh, and it's a fantastic movie.