NBA Legend Charles Oakley -- Knicks Owner Is a 'Diva'

Knicks owner James Dolan has something in common with Mariah Carey ... he's a huge DIVA .. so says Knicks legend Charles Oakley who says Dolan completely bungled an email situation with a fan.

Oakley -- who spent 10 years ballin' in Madison Square Garden -- tells TMZ Sports Dolan had some nerve ripping into a lifelong Knicks fan who had written a letter bitching about the team.

FYI -- Dolan called the fan a "sad person" and a "hateful mess" who makes his family miserable and is most likely an alcoholic. He also told the fan to go root for the Nets 'cause the Knicks don't want him.

Well, Oakley clearly took issue ... and chalked it up to typical "diva" behavior from another NBA owner.

One more shocking thing from this video ... Oakley, who spent nearly 20 years in the league, says he does NOT get free tickets to Knicks games ... and has tried to raise the issue with Knicks management.