they're called "inside jokes"
only blfians know about them
Well, by Dawkins categorisation, they're also memes.
Of course, Dawkins doesn't see our "joke memes" as being the only type of meme. Rather any idea/concept/behaviour that is spread within a community is a meme, whether it's a joke, or a dance, or a belief or more.
His whole idea is claiming their brown townogous to genes, and that they persist via a form of natural selection. Memes adapt over time to become interesting, or funny, or useful to a human, so that they can survive.
Our BLF jokes/memes are adapted to this community, but they wouldn't persist outside the community at all. They would need to adapt to be something more universally understandable/funny. Furthermore, they would be outcompeted outside this community, whereas here there are comparatively few memes, so they can flourish.
Also, if Kimon is going to stick to viewing Internet Memes through the eye of memetics, then he should likely be using Susan Blackmore's title for Internet Memes.
They're not "memes", they're "temes", because they're technologically carried memes.
So you better change the topic of the Tumblr megathred to the "Teme Megathread".