What should I do about my disrespectful brother?

I am the oldest sister in the family and my brother is the youngest of 19 years of age, soon to be 20. I get so frustrated and irritated of him. He is disrespectful and has a huge attitude problem. No matter what I say to him, it goes out the other ear. He doesn't fully realize how he is acting and when told upon he tries to argue back and defend himself right, when obviously he is wrong. He doesn't even consider the other person's side, just himself. He's that selfish, greedy, and cheap as well. As an older sister I don't know what to do with him anymore, he just doesn't listen. I try to talk to him and get his mind straight, but whatever I do he doesn't listen or even consider what I have to say. It just goes out the other ear. He is on my last nerve. My parents can't even do anything about it anymore. They gave up and lost hope in him and I'm seriously starting to too. Not even his closest cousin could get through to him. He's still the same when my cousin lectures him about life. I SERIOUSLY don't know what to do anymore. Please what can I do to change his disrespectful, bad attitude, and selfish ways?? Any advice is much appreciated. If I don't start changing him now, then he will lose a lot of friends and family. Thank you for reading.