Shampoo, it's a 1971 film, IMDB link. You can stream it for free if you have Amazon Prime. I just stumbled upon it.

Mostly entertainment value. This natrual 30-something beverly hills hairdresser is sleeping with many of his clients. He's not very good at cutting free needy women - I was grimacing the first ten minutes of the film. But I guess if I was dating an up-and-coming movie star I might accept her neediness... Hard to say. At one point he's sleeping with the wife, the mistress and the daughter of a businessman he's getting a loan from. Comical.