It was a dark Saturday night last month on the Lower East Side of Manhattan, where Saturday nights can get very dark, but Sabrina Brier, in a rhinestone necklace and strapless plaid pantsuit, was agleam onstage at a basement comedy club called Caveat warming up the crowd.

“You’re the butter, I’m the microwave,” she announced.

That particular joke passed quickly, but the metaphor hung in the air. After some years sweating on the back burner of show business, Ms. Brier, 28, has found instant success on the social media platform of the moment, TikTok. She has over 400,000 followers, and many more fans who view, “like” and share her videos, which mostly parody life as a young woman of some privilege and erratic self-confidence vacillating between the excitement of the city and the reassuring comforts of suburbia. (“You see this nook? Perfect for a pumpkin,” she declared in one about reclaiming fall, the supposed favorite season of “basic” white women. “Don’t blame me, blame the architect!”)

Ms. Brier specializes in point of view, or P.O.V., videos that confront relatable, often hateable characters, with a subtle sneer, gleefully rubbery body and arch delivery of generational catchphrases like “slay, queen” and “I got you,” often repeated for effect. She recently spoofed the Get Ready With Me (GR.W.M.) genre that has women across America smearing makeup on their faces, plugging beauty products and oversharing in equal measure.

P.O.V. of that GR.W.M.: “the girl who bullied you in high school is trying to be an influencer.”

In a five-part series on the “Extremely Passive Aggressive Roommate,” Ms. Brier pretends not to care about taking out the trash when it isn’t her day; enforces a rule about not having people over on weeknights; complains about her roomie coming home at 3:27 a.m.; strong-arms that roommate into renewing their lease and then welcomes a guest to “the common space.” (The first three videos have each been seen millions of times.) Ms. Brier’s own real-life roommate, Alice Duchen, an I.C.U. nurse, is often behind the camera, deadpan.

The two women live in Greenwich Village, near a rack of CitiBikes (Ms. Brier has also sent up the CitiBike poser who ostentatiously bleats “on your left!”), in a small two-bedroom walk-up apartment. She’s on a lower floor than the character she plays in one of her most popular videos, who breathlessly urges a visitor to ascend six flights of stairs in a building she’s trying to argue is luxury: “It’s going to be so worth it! Come on!”

Eleven days before the Caveat comedy show, Ms. Brier sat in her apartment’s dining area before a plate of untouched cookies, under a collection of paintings by her paternal grandmother, and told her origin story.

Her mother, Susan Cinoman, is a playwright currently working on a feminist retelling of the King Arthur legend who divorced Ms. Brier’s father, a cardiologist, when she was 5. “Very cordial,” Ms. Brier said. “Not any big drama.”

She has an older sister, Gabrielle, now a producer, and they were obsessed with Disney Channel when little, staging a modern-day “Cinderella “— “except instead of the ball it’s like a Britney Spears concert” — and later “rom-com girlie movies” like “Clueless” and “Mean Girls.”

Ms. Brier was in the sixth grade when she first got a phone, the Verizon Chocolate. “We were the A.I.M. generation,” she said, never dreaming that a phone could one day be a portal to everything. She attended Amity High School, where she won first place in a Shakespeare competition with a monologue from “The Taming of the Shrew,” not sure comedy was her winning strategy. “It was such a thing where the boys were the ones who got to have the personality, right? The boys were the class clowns.” She loosened up at Smith College, an all-women’s liberal arts college, where she majored in theater and took improv classes.

“It was always easy to identify her as someone who was performative,” Ms. Cinoman said on the phone. “She wasn’t an extrovert per se, but half of Sabrina was looking out the window at all times,Some other set of realities were impinging on the one that we were all in with her.”

After graduation, Ms. Brier worked in talent management for two years, and then got an assistant job in the writers’ room of “For Life,” an ABC drama about a wrongfully convicted man who becomes a prison lawyer to exonerate himself. “I am a fiend for anything that makes me cry,” Ms. Brier said. “Inside every comedienne is a sad girl, and that’s definitely me.”

After one season, Covid arrived. Restless in quarantine, she began posting videos on Instagram, one of which got picked up by Barstool, the popular sports blog. But this was before Reels. “It would be kind of blurry, and it wasn’t translating, and I didn’t understand it, and felt old,” she said. Then she tossed up a few on TikTok, notably one in which she faux-naively referred to Houston Street in New York, which is pronounced How-ston, as Hew-ston. Boom.

As Ms. Brier expanded her oeuvre from the single note of a Connecticut transplant in New York into the complicated jazz of friendship, especially female friendship, she began getting recognized in restaurants and on sidewalks. Dixie D’Amelio, a princess of the platform, named her account a favorite to follow. The model Emily Ratajkowski used Ms. Brier’s voice-over for a video about being “perceived.” The playwright Jeremy O. Harris included her in his “Coronavirus Mixtape” posts, carousels of videos and memes Mr. Harris posted during lockdown.

Ms. Brier’s viral fame has caught the attention of brands that pay her to write comic bits featuring their products, how she now makes her living. The girl who once made a video about being “the ULTIMATE subway girl” who couldn’t swipe her MetroCard is now being hired to sell Subway sandwiches. (Other sponsorships include Bumble, Uno the board game and mirrored cellphone cases.)

But she dreams of having, and show-running, her own television program. In May, she’ll perform two nights as her character at Union Hall in Park Slope, Brooklyn — a neighborhood that character would probably struggle to find. Now represented by Creative Arts Agency, Ms. Brier is auditioning to play other parts as well.

In this town, after all, you still need ambition as well as an algorithm.

“People are like, ‘Wow, this is all happening,’” Ms. Brier said. “And I’m like, ‘This is just things working out the way I was trying to get them to work out. It’s not random.’”