Self-Pitying Son

I was listening to your self-pity podcast and it could be the manual my son has for himself. He is 25 years old and lives on his own. How do you deal with someone who is in the self-pity mode and has no desire to stop doing it. He calls and moans and groans and complains and tells me how awful and unfair his life is and I end up giving him unwanted advice or checking out emotionally. How do I deal with him.