Oedipus is the story of one man's pride and his subsequent fall. In the case of Teiresias, Oedipus is particularly cruel and arrogant. At first the he is thrilled that the blind prophet has come to speak to him. When Teiresias speaks the truth, Oedipus scoffs at and mocks him. It's true that the prophet speaks in veiled terms and is not quite as obvious as he could have been; however, that's no excuse for Oedipus to eventually hit the old man. The clearest method Oedipus uses to discredit Teiresias is to mock him as being ignorant. He makes fun of the prophet's blindness--a great irony to the audience, of course, because we know the blind man "sees" way more than Oedipus the seeing man. He makes fun of the prophet's age, implying he's to old to know what he's saying--another irony we can enjoy, for we know he's telling the truth. He mocks him as being a prophet who can't figuratively see anything important--and yet we know he sees the truth which Oedipus does not. Teiresias, despite the abuse, has spoken what he came to say and leaves with some dignity.