I don't think it's showing off. No one is excluded from adding to the joke or building on a meme, so long as it's funny. In that way, it's more meritocratic. Yes, you have to learn what the joke is about, and it creates its own culture and language and community, but that doesn't make it exclusionary just because it's not common knowledge. Exclusionary would be saying, "YOU can't say that because YOU are new here."