Title text:
In 1899, people were walking around shouting '23' at each other and laughing, and confused reporters were writing articles trying to figure out what it meant.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3184/
Funny enough, there's a point in a later book in the series where they suggest the "ultimate question'" that 42 is an answer to could be "What do you get if you multiply six by nine?"