Who is Epictetus talking to that he regarded as "unworthy"?
He's talking to the person who said, "tell me something!" This person really is not in a state of mind to learn and Epictetus proceeds to show this person why they are not ready to listen to Epictetus.
Skill is required to speak and to listen. And when it comes to listening, "a good deal of practice in listening" is required "if one is to listen to philosophers" (v. 10, p. 137).
Epictetus wants his listeners and his students to show some initiative in listening - in wanting to learn. To them he says, "Show me, then, what I can achieve by entering into a discussion with you. Excite some desire in me" (v. 15, p. 138). But if the person just sits around like a bump on a wall, saying "tell me something" then Epictetus wants nothing to do with them. In fact, he only has one thing to say to people like this:
whoever is ignorant of who he is, and what he was born for, and in what kind of world he finds himself, and with what people he is sharing his life, and what things are good or bad and what are honourable or shameful, and is someone who is incapable of following an argument or proof, and doesn’t know what is true or false, and cannot distinguish between them: such a person will exercise neither his desires, nor his aversions, nor his motives, nor his designs, nor his assent, not his dissent, in accordance with nature, but being altogether deaf and blind, he’ll go around thinking that he is somebody when in reality he is nobody at all. And do you suppose that there is anything new in this? Isn’t it the case that ever since the human race came into being, it is from this ignorance that all our errors and all our misfortunes have arisen? (v. 19-20, p. 138)
He concludes with, "When you want to know what a philosopher has to say, don't ask, 'Have you nothing to say to me?', but simply show that you're capable of listening to him" (v. 29, p. 139)