Bill O'Reilly, 2001 (emphasis mine):

The late-night program hosted by David Letterman is the toughest interview show on television. That's because Mr. Letterman is a smart guy who can spot a phony with telescopic accuracy and expects his guests to bring something to the table. If a guest begins to sink on this show, the bottom is a long way down.

Dave Letterman to Bill O'Reilly, 1-3-2006:

I have the feeling about 60 percent of what you say is crap.

In that same interview, O'Reilly repeated some bogus story about a school changing the lyrics to the song "Silent Night." Turns out the school was doing a Christmas play were one of the characters sings a song to the tune of Silent Night. And the play was written by a church choir director.