So… what does it actually mean?
Nothing. That’s the beauty of it. “6–7” isn’t a secret phrase, an acronym, or some coded reference. It’s just fun to say, easy to copy, and makes kids feel like they’re part of something. In other words, it’s classic internet humor: random, harmless, and over before parents even figure out what’s happening.
— Read on www.bitdefender.com/en-us/blog/hotforsecurity/why-your-kids-keep-saying-six-seven