Tumblr founder David Karp signed his note to Tumblr users about the Yahoo acquisition “Fuck yeah, David.” To those covering Tumblr from a remove, that may have seemed the brash sign-off of a young founder who will shortly pocket a cool $250 million.

They were wrong. It was actually a secret valentine to the Tumblr community, coded language that could only be understood from the inside. It referred very specifically to the viral, homegrown, NSFW, and much-beloved Tumblr in-joke: The “Fuck Yeah” meme.

The Fuck Yeah meme is native to Tumblr, one that replicated and mutated into thousands upon thousands of single-topic tumblrs all celebrated with the same enthusiastically profane prefix. It’s easy: whatever you are fucking-yeah to — let’s say “tomatoes,” because they are delicious — the formula goes like this: fuckyeahtomatoes.tumblr.com. There’s FuckYeahBeatles and FuckYeahShakespeare (“sonnets, quotes & shit”); FuckYeahRyanGosling and FuckYeahMetallica and FuckYeahBrusselsSprouts. There’s a FuckYeah for Harry Potter and pretty much every one of his friends at Hogwarts (FuckYeahGryffindor!). There’s FuckYeahStarWars and FuckYeahStarTrek; FuckYeahThe60s, FuckYeahThe70s, FuckYeahThe80s and FuckYeahThe90s;FuckYeahGameofThrones, FuckYeahParksAndRec, and FuckYeahGirls; FuckYeahCocoRocha and FuckYeahCommeDesGarcons (Tavi,is that you?); FuckYeahWesAnderson and FuckYeahBroadway and FuckYeahFeminism and the someone-had-to-do-it FuckYeahYeahYeahYeahs. There are the meta versions (FuckYeahFuckYeah) and PG versions (FYeah!). I started one with two friends in 2009 to celebrate awesome women of a certain age: FuckYeahThirties.

There are competing theories as to who or what started it — Tumblr’s now-defunct Storyboard department explored it in graph form (here and above) and placed its origin in April 2007 with fuckyeahtechnospeedandgirls.tumblr.com (enjoy it, legacy Yahoo users!). But it was FuckYeahSharks, launched in October 2008 by writer and Tumblr denizen Ned Hepburn, that turned it into an in-joke Tumblr sensation. Per the Storyboard timeline: “Only the 40th fuckyeah Tumblr to date, it will arguably define the genre.”

By April 2009, the genre had exploded, with 25 new Fuck Yeah tumblrs created daily. (NB: April 2009 was also the tipping point for Twitter, when Oprah joined and Ashton Kutcher and CNN had their race to a million followers. Ah, the good old days.) By mid-May, there was an official Tumblr Fuck Yeah directory (formerly at http://www.tumblr.com/directory/fuckyeah,it now redirects to http://www.tumblr.com/spotlight). And by June, it was impossible for anyone on the Tumblr dashboard semi-regularly to have missed the trend. (I proved that point - here is my June 2009 post about how sharks love David Hasselhoff.)

One need only glance at the graph above — or have a clue about memes at all — to know the rest. Fuck Yeah went viral on Tumblr, climbing steadily as Tumblr’s favorite in-joke, kept as its own thanks to the media’s confusion over how to cover such an explicitly profane viral sensation. (It never did get its NYT Sunday Styles piece.)

Ergo, Karp’s sign off. He’s not just the founder of Tumblr, he’s been a presence on it every single day. (See Marco Arment on this.) There’s a FuckYeahDavidKarp, too — a joke that everyone gets because of Karp’s early, authentic engagement with his community.When you signed up for Tumblr, you auto-followed staff.tumblr.com, which often reblogged david.tumblr.com, along with a recognizable shaggy-haired cartoon avatar. That’s Karp, and if you click on it right now you’ll come to last night’s entry citing Tumblr’s Webby acceptance speech: “Fuck yeah! Fuck yeah! Fuck!”

That’s the origin of “Fuck yeah, David.” Anyone who took it as a “fuck you” does not get Tumblr, or, in a larger sense, the shared connections that bond communities. Even though I no longer spend hours on the dashboard hearting and reblogging, as a Tumblr user from late 2008, I instantly got that sign off and am still connected to what it meant.

It meant, “Fuck yeah — this is still ours.”

Rachel Sklar is a writer and the co-founder of TheLi.st. She invites you to browse Fuck Yeah selections curated by Urlesque, Mashable, and Flavorwire. She is still proud of her contribution to this trend. Fuck yeah Amy Poehler.