NEW YORK (CBSNewYork/AP) — This isn’t a good look for New York Knicks owner James Dolan.

The oft-embattled Madison Square Garden chairman responded to a Knicks fan who had criticized him with an email wondering if the man is an alcoholic and telling him to root for the Nets instead. An MSG spokesman confirmed the email, which appeared Sunday on Deadspin.com, was written by Dolan.

Dolan called the father of filmmaker Aaron Bierman a “hateful mess” and a “negative force” to anyone with whom he comes into contact.

The elder Bierman had written Dolan and said he was a Knicks since 1952 who was tired of Dolan’s management of the team and urging him to sell.

“As a Knicks fan for in excess of 60 years, I am utterly embarrassed by your dealings with the Knicks,” he wrote in part. “Sell them so their fans can at least look forward to growing them in a positive direction Obviously, money IS NOT THE ONLY THING. You have done a lot of utterly STUPID business things with the franchise. Please NO MORE.”

Dolan responded: “You are a sad person. Why would anybody write such a hateful letter. I am.just guessing but ill bet your life is a mess and you are a hateful mess. What have you done that anyone would consider positive or nice. I am betting nothing. In fact ill bet you are negative force in everyone who comes in contact with you. You most likely have made your family miserable. Alcoholic maybe. I just celebrated my 21 year anniversary of sobriety. You should try it. Maybe it will help you become a person that folks would like to have around. In the mean while start rooting.for the Nets because the Knicks dont want you. (sic)”

Dolan has been in charge of the Knicks since 1999.

On Monday, Bierman told radio stations WFAN and 1010 WINS that he was shocked by Dolan’s response.

AUDIO: 1010 WINS Interviews Irving Bierman

“I wasn’t being disrespectful,” he told 1010 WINS. “I was being 100 percent professional, unlike him.”

He added on WFAN’s “Boomer & Carton” show: “To me, it was a joke. Everything he said to me was a joke. It had nothing to do with (what I wrote) in my original email.”

His reply?

“I said ‘Thank you and good luck,’ ” Bierman said.

(TM and © Copyright 2015 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2015 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)