What's the meme?
6 7
Now get off my lawn, Shorty... or pick up the phone.
A linguist goes into the meme and it's history:
* https://www.youtube.com/watch?v=laZpTO7IFtA
You not getting it is the main point of the saying: it's slang term that young folks (in-group) are using to differentiate themselves from the not-young folks (out-group).
I'm just waiting for Sesame Street to declare 6 and 7 the numbers of the day.