"An Ideal Husband" - Oscar Wilde

Mabel: You are very late! Lord Arthur
Goring: Have you missed me?
Mabel: Awfully! Lord Arthur
Goring: Then I am sorry I did not stay away longer. I like being missed.
Mabel: How very selfish of you! Lord Arthur Goring: I am very selfish. Mabel: You are always telling me of your bad qualities, Lord Goring.
Lord Arthur Goring: I have only told you half of them as yet, Miss Mabel!
Mabel: Really! Are the others very bad?
Lord Arthur Goring: Quite dreadful! When I think of them at night, I go to sleep at once.

Lord Arthur Goring: I'm sorry, Father, but the truth is, this is not my day for talking seriously.
Lord Caversham: Well, what do you mean, sir?
Lord Arthur Goring: I mean that I only talk seriously on the first Tuesday of every month. Between noon and three.

Lord Caversham: What are you doing here, sir? Wasting your time, as usual?
Lord Arthur Goring: My dear father, when a man pays a visit, it is for the purpose of wasting other people's time and not one's own.
Lord Goring: You see, Phipps, Fashion is what one wears oneself. What is unfashionable is what other people wear. Phipps: Yes, my lord. Lord Goring: Just as vulgarity is simply the conduct of other people. Phipps: Yes, my lord. Lord Goring: Other people are quite dreadful. The only possible society is oneself. Phipps: Yes, my lord. Lord Goring: To love oneself is the beginning of a life-long romance, Phipps. Phipps: Yes, my lord.

And my favourite:
Mabel: To look at a thing is quite different from seeing a thing, and one does not see anything until one sees its beauty.