“six-seven” has taken over elementary and middle schools in America. It’s everywhere.
Here’s a clip from a recent south park episode with six-seven.
And here’s a recent xkcd:
And here’s a six-seven character from Roblox:
Be thankful if you aren’t around kids constantly shouting “six-seven!” at each other and laughing.
As a Gen-X I’ve annoyed the Millennials around me at work by fully embracing “67” any time I pick up on it, just like I’ve done all the others mentioned in the XKCD. I’ve never stopped a few of them, like “42”, “1337”, and “58008”. But those were from MY generation and fellow geek community, so there’s that.