To me, the play to begin with when teaching the representation of sex and sexuality in the theatre is La Dame aux Camélias or Camille by Alexandre Dumas fils. The reasons for this are many.
First, Camille's plot is the basis of all hooker-with-a-heart-of-gold plots. To name only the most famous: La Traviata, Moulin Rouge, Pretty Woman, and Rent all owe their plots to Camille's narrative.
Second, Camille's attitude toward sex is a complicated one. The play loves its heroine, Marguerite Gautier. She is a big ol' whore and the play has a great time sharing with the audience the pleasure of being a whore. And then, of course, the heroine must die. She is punished for her sexuality at the same time as the play itself cashes in on that sexuality. It's an extraordinary dramaturgical move that, frankly, I am not even sure Dumas fils knows he is making.
What I really love about the play, though, is Dumas fils's absolutely sparkling dialogue and wit. Take for example, the play's first scene. Marguerite enters to find the Baron de Varville (who is, basically, a whiner) waiting for her to come home, as he always does. As she enters, the Baron complains:
Varville: Is it not my fate to be always waiting for you?
Marguerite: Is it my fate never to come in without finding you here?
Varville: Is it my fault that I love you?
Marguerite: My dear friend, if I were to listen to all the people who are in love with me, I should have no time for dinner. I allow you to come here at any hour when I am at home and to wait for me whenever I am out, but if you will persist in talking of nothing but your love, I must withdraw my friendship.
Varville: And yet, Marguerite, last year at Bagnères, you did give me a little hope.
Marguerite: My dear, that was at Bagnères, when I was ill and bored; this is Paris—I am much better and not at all bored.
Later in the scene, Marguerite is told that a new character, Armand Duval – whom she has just met – visited her every day for a year when she was ill but never left his name. She calls to him across the room and uses this occasion to further beat down the Baron de Varville:
Marguerite: M. Duval, do you know what I have just been hearing? That you called to enquire after me every day when I was ill.
Armand: It is quite true.
Marguerite: Then the least I can do is thank you. Did you hear that, Varville? You never did that for me, did you?
Varville: I've only known you for a year.
Marguerite: Don't be silly. This young gentleman has only known me five minutes.
At any rate, I adore her and find the play delightful.