One of the most enduring reasons for Buffy the Vampire Slayer's continued success lies in its witty dialogue, which has created authentic interpersonal relationships, dramatic tension, and a multitude of hilarious inside-jokes. It's the inside-jokes that make the Buffyverse feel like a real place, where these characters not only actually exist fighting the supernatural forces of darkness, but also interact in a way that feels plausible.
The series about a teenage vampire slayer and her friends fighting creatures and creeps in smalltown California mirrored the trials and tribulations of adolescence. Joss Whedon tapped into teenage fears and magnified them in his representations of vampires, ghouls, and demons. The jokes penetrated the darkness, and like the series itself, became relatable to fans. The inside-jokes connect the characters to one another, and the fans to the fandom. Find them explained below.
10 MR. POINTY
In Season 2, Kendra tells Buffy the name of her favorite stake, "Mr. Pointy". In the season 2 finale, just before she passes, she gives her stake to Buffy as a good luck charm and to remind her of her purpose. From then on, Mr. Pointy is referenced in passing by many characters.
In Season 3, Buffy tells Angel that she doesn't want to end up at a Retirement Home for Slayers, with a bronzed version of Mr. Pointy that she uses to regale her crusty peers with. Buffy has admitted to Mr. Pointy being like her security blanket when she doesn't feel at her strongest.
Though "Bunnies" are technically first brought up by Oz, it's Anya the vengeance demon that makes them a recurring joke among the Scoobies. During the Halloween episode of Season 4, Anya dresses up as the most horrifying creature she can imagine - a bunny.
She referred to "cults of bunny worshippers" as her greatest nightmare, and in Season 5, she both found a stuffed bunny that she took as a harbinger of doom, and also sang about how evil bunnies were in the musical episode. In Season 6, she accidentally summoned dozens of the furry fiends, and in Season 7 the mention of bunnies gave her enough determination to fight her enemies.
8 THE SCOOBIES
Buffy fans refer to the group of supernatural fighters Buffy, Willow, Xander, and Giles as the "Scooby Gang" after the famous teenage sleuths in Scooby Doo Mysteries. Other members were added as the series progressed such as Anya, Tara, Dawn, Spike, etc.
The group also refers to themselves as the Scooby Gang, or "Scoobies", especially when it comes to amassing for a briefing our council about how best to take on an otherworldly opponent. This is especially apropos given that Sarah Michelle Gellar played Daphne in the live-action Scooby Doo movie while Buffy the Vampire Slayer was still on the air.
7 A THING
"A thing" is used by characters in the series to either avoid discussing a particular topic or make an excuse for them to leave an area. The phrase, "It's a thing" or "I have a thing" are considered perfectly reasonable explanations by the Scooby Gang in most situations.
When Xander wants to ask Buffy to the prom early in the series, he asks Willow, "Don't you have a thing?" to which she replies, "A thing! The thing! That I have! Which is...a thing that I have to go to.". When Buffy tries to get out of a date with Ted she says she would love to go, but she has "a thing on Saturday" to which the Scoobies dutifully confirm. She also gets Spike out of the house in front of social workers by asking him if he has "that thing" to do.
In the Buffyverse, almost any terrible supernatural force of evil you can think of will show up in Sunnydale. Ghosts, goblins, demons, witches, vampires, and even the Cheese Man (a mysterious entity who appeared to members of the Scooby Gang in a dream) want to tap into the Hellmouth beneath it.
To give some sort of sense of authenticity to a universe with that many mythical entities, Leprechauns are only ever mentioned as fictitious. In Season 3, Buffy explains, "There are two things I don't believe in: coincidence, and leprechauns."
5 THE WORLD WITHOUT SHRIMP
The World Without Shrimp or conversely The World With Nothing But Shrimp was brought up to represent alternate dimensions and is brought up by various characters in episodes dealing with parallel realities, timelines, or alternate versions of existence.
Xander brought it up in Season 5 and made Anya obsess about it, Willow has brought up being able to communicate with the likes of shrimp, and the followers of Connor were sent to a shrimp world to protect them from spending eternity in Quor'toth, the darkest of dark worlds and a hell dimension.
4 BOSS OF ME
"Boss of me" and its iterations is a phrase used both in a positive and a petulant sense depending on the situation. For instance, in Season 3, Xander rebuffs Giles' scolding by declaring, "You're not the Watcher of me". In the same season, Willow says, "Of the two of us here, which is the boss of me?".
After Buffy's death in Season 5, the Scooby Gang has an argument about leadership. Xander asks who made Anya the "boss of the group". Tara pipes in that Willow should be boss because she had received a little glittery plaque that said "Boss of Us" in reference to her constant confusion.
3 STAR TREK
It's no secret that Buffy creator Joss Whedon is a huge Star Trek fan, and references to Star Trek are peppered throughout the series, mostly by the "nerdier" characters like Xander, Willow, and Andrew. Xander even refers to the inscrutable Giles as "Locutus of Borg", in reference to when Captain Picard got assimilated by the Collective in Star Trek: The Next Generation.
There are several references to Klingons when vampires get the "forehead ridges" when they fang out, and Andrew has a "man-crush" on Captain Archer, Scott Bakula's character in Star Trek: Enterprise. Xander at times teases him about it.
2 STAR WARS
Besides being a Trekkie, Joss Whedon is also a big Star Wars fan. One of the biggest homages to this is the giant Death Star painted on the side of the van used by the Trio. The horn even plays the Star Wars theme song. Warren, Jonathan, and Andrew view themselves as epic villains on par with the Emperor and Darth Vader.
When Spike consults the Trio to get their help in making a Buffy Bot for his personal use, they initially refuse, until he holds up a priceless Boba Fett action figure and threatens to snap it in two. They quickly change their minds. After The Phantom Menace came out, there were also loads of inside jokes in Angel.
Before Joss Whedon would go on to direct his first Avengers movie for Marvel Studios, he would pepper his series with references to the Caped Crusader of DC Comics. When Spike first got his crypt it was referred to as the "Batcave" by a snickering Xander.
Spike has always made fun of Angel's brooding nature, comparing his stalking the shadows, protecting his loved ones from afar without getting too close, and wallowing in self-pity as traits of the Dark Knight. He even calls Angel's car "the Angelmobile".