1063
xkcd #3184: Funny Numbers
(imgs.xkcd.com)
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/
6-7 is an under 10 thing. By the time you're 12, it's stupid.
Nah, even early 20s do it here.