>>108380978afaik it was a clip from a rap song that was used as a bgm for a tiktok video that went viral. The tiktok discovery algorithm got confused because it couldn't differentiate bgm lyrics from actual spoken-word content in videos, and mistakenly boosted the discovery of every video that said "67"
Tiktokers realized the bug and so started just randomly saying 67 in all of their videos for a free algo boost
Zoomers not understanding how algorithms worked assumed it was some kind of in-joke and started imitating it
And now it's a meme to just randomly say 67 as a non-sequitur and pretend like people who are confused by this baffling behaviour are not 'in on the joke'