What exactly is Oprah Winfrey's problem with David Letterman?

In all the stories about her ballyhooed appearance on Thursday night's "Late Show" (11:35 p.m. on CBS) -- her first on a Letterman show in 16 years -- I have yet to read a satisfactory explanation for why she has avoided Dave's show for all that time.

Theories abound, however.

One of them holds that Oprah was embarrassed by Dave's infamous "Oprah, Uma; Uma, Oprah" line at the 1995 Academy Awards, which Dave hosted.

More than 10 years later, it's still a sore subject for Oprah and Uma Thurman, who share a sensitivity about their unusual names.

"You remember that night, don't you?" Oprah asked Uma on her show in October.

"How could I forget it?" answered Uma.

"This is the thing, you have an unusual name too," said Oprah. "Did you always love your name?"

"No," said Uma, shaking her head vigorously.

"Just like I didn't either!" Oprah replied.

Poor babies.

Under another theory floated recently, Oprah is still smarting from her last appearance -- one of only two she has ever made -- on May 2, 1989, when NBC's "Late Night" originated from the Chicago Theatre during a visit to the Windy City.

Chicago Tribune TV columnist Phil Rosenthal last week unearthed his paper's coverage of the show from that date (He has access to the Tribune archives; I don't. Moreover, our own archives indicate that The Post ignored Dave's 1989 visit to Chicago entirely).

According to the Tribune, Oprah had a rough time. Reported the Trib, "[Letterman] couldn't help that his interview with Oprah Winfrey uncomfortably disintegrated into discussions of black people in restaurants, satanic sacrifices and one scream [from the audience] of, 'Rip her, Dave!"

For this off-night, Oprah sentenced Dave to a 16-year snubbing? I can hardly believe that an individual of Oprah's stature can be so spiteful! (I'm being sarcastic, of course).

"I've done the show twice," Oprah told Time magazine in December 2003, when she was asked about Dave. "Both times I was sort of like the butt of his jokes. I felt completely uncomfortable sitting in that chair, and I vowed I would not ever put myself in that position again!"

There you have it -- the real truth about the Queen of Daytime: Basically, she has no sense of humor whatsoever.

Rip her, Dave!