So first, I'm going to be up front - I am not a linguist, so I am going off of my special interest knowledge. Any linguists out here are more than free to correct me on anything I get incorrect about idiolects and dialects, this is my amateur opinion as someone who has been on this webbed site since 2014.
Yeah, accents are how we pronounce words, and yes, it's not the best term for the phenomenon referenced by OP. And I'm not going to argue with an expert's definition of idiolect, however, I am going to point something out about your definition of "small."
Tumblr's user base is small only in comparison to social media sites like Facebook, Twitter, or TikTok. According to SQ Magazine, in 2025 there were 12 million daily active users from the U.S. alone. It we assume that say, only a tenth of those users find themselves referencing the plinko horse in casual conversation, that's 1.2 million people. For reference, the "Hoi Toider" family of dialects from the Outer Banks of North Carolina is spoken by maybe less than a couple thousand people? (I've seen the number 150 floated, but I'm pretty sure that's just from one island - geographically the accent is spread out over several islands of the Outer Banks and some limited areas of the mainland.) Personally, I think once we've gone over a thousand people, we're out of the "small" category anyway.
Plus, the examples given by your professor (school, company, family) generally include elements of direct proximity or some sort of specific geographic anchor point. They all are going to be made up of people who live in close proximity to one another and/or who return to a centralized location more often than not. There's also a centralized hierarchy of authority figures that form the nucleus of the unit, whether that's a school administration, executives and managers in a company, or parents/elders in a family.
And I was actually thinking about this already, but arguably, Tumblr's particular vernacular may just extend to pronunciation/enunciation even though it's not actually an accent! Our ludicrous speech patterns are shaped by the fact that Tumblr is heavily text-based. Text really is the preferred mode of communication, with lots of visual modifiers and enduring meme references that indicate tone and subtext.
That's where subvocalization comes in. Subvocalization is where your larynx (voice box) and other muscles involved in speech actually move as if forming words while you read. You generally cannot feel it, but subvocalization can be detected by specialized machines.
You know how people learning to read usually have to start out reading out loud before they can read silently? Reading is actually a VERY complicated cognitive skill, in no small part because rendering spoken language into symbols adds a lot of cognitive load to your brain, especially to your working memory. It's thought that subvocalization helps lighten the load because you may not realize it, but your throat is silently creating the sounds of the words you're reading. You get physical feedback that might act as a memory aid.
Now what does that have to do with the Hellsite Vernacular?
Read the following examples to yourself out loud:
5. I think ☝️ I have covid.
6. I 👏think 👏I 👏have 👏covid.
Yes, you could read all of these statements completely flat, ignoring the visual shenanigans and formatting, but, more than likely, you ended up preserving the gags in your verbalization because each one is communicating different information! In example 2, you probably preserved the misspelling as a diphthong because that's part of the joke. Number 3 you might read as basically one word because there's no spaces. Number 4 might have some variation in interpretation, but I usually read it in a jerky cadence with my pitch going up on capital letters and lower on lower case letters. Other people might get louder on capitals and softer on lowers or use the capitalization pattern to determine stress patterns. You might have interpreted the emojis as punctuation marks, or used them as theatrical directions.
And even if you didn't say those phrases out loud - you still used subvocalization to help map what they should sound like.
For visual gags like emojis, formatting, and spellings, you're going to tend to say them out loud the way you silently read them because you're already basically practicing them via subvocalization. When I perform the ole Random Capitalization gag out loud, I emphasize the capitalized words because that's how I read them silently. When I verbalize the clap-emoji joke, I either punctuate each word or actually clap. For memes based on short videos or performances like "the sacred texts!" or "okay, noun-boy" the tendency is probably to preserve the original cadence and tone of the source meme.
Now yeah, specific enunciation choices can differ person to person, but if spoken aloud, we're still trying to preserve the information that each differing format would communicate to another Tumblrina. Speaking Tumblrish will have you using enunciation and pronunciation outside of your typical accent. And all of that is on top of the syntax gags and verbiage that's more classically associated with Cringe Unhinged Microblogging English.
But no, I do agree that in technical terms, "accent" isn't the most accurate description of what's going on, however, I do argue that we're not just a bunch of individuals or small groups - Tumblr is a community. We have a shared culture, history, and lingua franca even when we might hold wildly different opinions on like say, trans women and their rights to not have all their posts marked mature or have their accounts deactivated on a whim. (Yes, @staff, I'm staring right at you, you've been doing okay on not fuckin up the UI lately but we all know you can do better.) And this community is in reality, pretty large, geographically spread out with no central anchor or authority figures, has multiple sub-cultures, and in practice, speaks with multiple distinct accents even when we might sometimes share enunciation and pronunciation references.
Idiolect is too narrow, accent doesn't actually encompass what's going on - in my opinion, we should call it a dialect or vernacular.
But! ☝️This is also Tumblr, where the humor is in the text gags. In the gaining net zero information on posts, the Vanilla Extract, the rent lowering shots, the color of the sky, and the Goncherovs. Our cultural pastimes are posting a photo with a blatant lies attached a la Bitch, That's The Tubby Custard Machine and That's Not Were-Ralph That's Adam Driver, creating wacky bracket challenges like deciding a Tumblr Sexyman or Tumblr's Most Breedable Man, celebrating holidays from the joyously adorable to the laughably absurd such as Neil Banging Out the Tunes and the Ides of March, and we still tend to communicate important news to one another via Jensen Ackles's emotionally constipated face.
"Hellsite Vernacular" or "Cringe Unhinged Microblogging English (CUME)" might be more accurate, but insisting on an inaccurate name that communicates incorrect information is very On Brand for us.
Long live the Tumblr Accent, may I always show up to this particular devil's sacrament.
