One of the series' most memorable moments occurred in the mid-1990s when Johnny Carson made a surprise walk-on appearance. David Letterman stood up and let Carson sit at his desk for a moment, with the intent of having the The Tonight Show Starring Johnny Carson (1962) veteran deliver a joke. The audience went crazy and applauded for so long that Carson never got to say a word.
In the wake of the September 11, 2001 attacks (specifically the World Trade Center attack in New York, downtown from where "The Late Show" is taped), David Letterman was reported to have said that he didn't know if anything would ever be funny again. Most American programming (including "The Late Show") was suspended in the aftermath. However, on September 17, "The Late Show" was one of the first comedy shows to resume regular programming. The starting guest that night was Dan Rather, and the emotionally-charged episode is considered one of Letterman's finest.
On the show, people in the audience are often wearing coats, or appear "bundled up". This is because the temperature of the Ed Sullivan Theatre is kept at 58 degrees during taping, supposedly at Dave's insistence.
Before reading the Top Ten List, David Letterman used to announce that it came "from the home office of Sioux City, Iowa". This was a reference to the fact that at the time, the CBS affiliate in Sioux City refused to air the show.
On April 28, 2010, Letterman's monologue included references to Jay Leno's 60th birthday. He refused to read one joke from the cue cards. The joke was: "Time flies - seems like just yesterday he was pushing Johnny out."
When Louis C.K. requested to be booked on the show, the producers asked if he would meet with Letterman to discuss being hired as a writer. C.K. agreed to this only if he was given a firm date to perform on the show. C.K. had no intention of writing for the show but upon meeting Letterman he could not turn the offer down. C.K. hated the job and quit after three months.
NBC claimed "intellectual property rights" on many of Letterman's famous running gags and characters from his original show. As a result, the character of "Larry Bud Melman" was retired (though the actor remained with the show and appeared under his real name), and such traditions as "Viewer Mail", "Stupid Pet Tricks", and the "Top 10 List" were simply renamed. This controversy was the subject of much ridicule during the 1993-94 TV season, mostly from Letterman himself.
The microphone on David Letterman's desk is an old RCA DX 77. It is a replacement for the original microphone given to him as a gift from the NBC crew when he left the network. A couple of years after making the move to CBS, the original microphone was stolen. The microphone on his desk is usually not plugged in. His primary microphone is the lapel clipped to his tie.