When he was eyeing Takei as his celebrity cameo of choice, O’Brien was missing one crucial piece of information, and it proved to be the entire reason the actor passed on appearing in the episode. As Conan told The Ringer:
“We were all stunned. ‘What do you mean George Takei said no?!’ I didn’t know what he was doing at the time. Then it came back to us that George Takei was somehow affiliated with the San Francisco Board of Transportation. He thought that this was maybe making fun of public transportation.
Obviously, public transportation itself was never the target of the former “Saturday Night Live” and “Simpsons” writer’s humor. As usual, the townsfolk of Springfield were set to be the butt of the joke. But given his position as the face of San Francisco’s public transit, it’s understandable that Takei might not have wanted to seem to be taking potshots at affordable modes of travel. It didn’t take long for Conan and the “Simpsons” staff to find their replacement, though. Literally the next day, according to the late-night comedy legend, he was informed that Nimoy was ready and willing to fill Takei’s “Star Trek”-shaped void. And that was just fine with Conan, who noted one very important fact about Mr. Spock: “He outranked Sulu.”