Master Kaymo: Christopher Rowley, in honor of the insane god Kaymo from his Basil Broketail books.
Niko "Dal'Ariel" : A fanon "surname" for Niko, created for an old fanfic. It just translates to "Student of Ariel"
"Eric" Wheiner: Fanon's first name for Senator Wheiner.
The Land of Aaa: Supposedly a Rule 63 version of Ooo where Fiona, Cake et al. live. Note that in canon, the Ice King refers to them living in Ooo.
Farmworld: The alternate timeline where the Lich never existed, as seen in "The Lich," "Finn the Human" and "Jake the Dog." So named because this reality has Finn and a non-sapient Jake living in a farming community.
Ice King Finn/Ice Prince: This world's version of Finn after he puts on the Ice King's crown.
Zuzu: Originally used by Azula, but eventually picked up by the fangirls due to his Adorkableness.
Possible Unfortunate Implications here, as "Zuzu" is also one of the nicknames for erotic fanfiction pairing Azula with Zuko... often in the form of the latter being forcefully dominated by the former...
Frothers, Foamy, Foaming Mouth Guy, Rabid Fanboy: Nickname given to a nameless character whose only defined trait was to collapse into a frothing seizure upon mention of the Avatar.
Koizilla: The ocean spirit's One-Winged Angel form in the Season 1 finale. This actually came from a production nickname.
Nmokas: Nameless Mother of Katara and Sokka. Her name is revealed to be Kya late into the final season.
June the bounty hunter is sometimes referred to as "The Patron Saint of Zutara" from the way she refers to Katara as Zuko's girlfriend. Repeatedly.
Firelord Susan: Mondegreen of Firelord Sozin, heard in the beginning of "The Avatar and the Firelord" among others.
Fatherlord: Ozai, adopted by some boards after Zuko's unfortunate slip-up in the finale.
Avatar Susan: Used by some fans to refer to Avatar Yangchen, who appeared in flashbacks before being named in the series finale.
Comes from SDCC 2007, where one of the finalists in the costume contest dressed as her and the panelists called her "Avatar Susan" when listing off the costumes.
The Gaang: Aang and his group — Katara, Sokka, Toph, and later on, Suki and Zuko. Acknowledged on the front cover◊ of an issue of Nick Mag dedicated entirely to the show, and a little later in the show itself:
Sokka: I just wanted to say, good effort out there today, Team Avatar! Katara: Enough with the Team Avatar stuff! No matter how many times you say it, it's not gonna catch on. Beat Sokka: The Aang Gang? Katara: Sokka...
Ozai's Angels: Azula's group. Helped out by pictures like this.
And the fact that the meta-tastic The Ember Island Players outright acknowledges the nickname by having the actresses playing Azula, Mai, and Ty Lee in the play do the Charlie's Angels Pose at one point.
The Dangerous Ladies: The other name for Azula, Mai, and Ty Lee. This was probably coined in-show, in "The Chase".
Sokka: Has anyone given thought to the tankful of dangerous ladies that seem to be after us?
The apparent similarities between Azula, Mai and Ty Lee with Haruhi, Yuki and Mikuru respectively has led to the coining of the term Hare Hare Ozai.
The Zucrew: Zuko, Azula, Ty Lee and Mai in the first half of Season 3.
Development and Production
Bryke: Collective name for series creators Bryan Konietzko and Michael Dante DiMartino. Alternately, the name of the ultimateCrack Pairing.
"The Creators" is an older name for them, although it fell out of use with the coining of "Bryke".
Avatar Withdrawal Syndrome (AWS): It refers to the long hiatus between the end of Season 2 and the beginning of Season 3. It's also occasionally invoked during the wait between the first and second halves of Season 3.
Avastaff: Refers to Mike and Bryan and their underlings. This name was invoked mostly during the wait between Seasons 2 and 3 (as in, "the Avastaff need to get their heads out of their asses and make some new episodes!").
Events and Concepts
Aangst: Aang's multiple bouts into angst territory, Season 2 and onwards.
Momoments: Coined by the creators for funny or interesting clips involving Momo.
Zuko Planned It (ZPI): Used by fans who refused to believe that Zuko was actually evil in the wake of his failed Heel-Face Turn at the end of Season 2.
Shamwow: Coined by Penny Arcade and adopted by CAPSLOCK_ATLA for director M. Night Shyamalan after the Live-Action Adaptation. Also called Shamallama and Shamalamadingdong by those who both scorn him and have trouble pronouncing his name.
Avafan: A fan of the series. Avafan describes more casual fans...
Avatard: ...while Avatard is used for the hardcore set.
Cloudbaby: A theoretical child of Aang and Katara (air + water = clouds). Used mostly for Original Characters, though the term can now also be applied to Tenzin, Kya II and Bumi II, their canonical children.
...Whereas "Steambaby" refers to a theoretical Zuko/Katara spawn. A "Ninjababy" would be a Zuko/Mai kid. An Aang/Toph baby would be called a Dustbaby.
So if Katara has kids with Haru, or some other Earth Nation guy, they'd have Mudbabies, yes?
Avatar: The Legend Of Korra
Brolin: Due to giving the appearance of a true bro.
The Korralition: The Korra-coalition, a nickname for the group of protagonists to go along with "the Gaang."
Every time Lin Beifong shows off a new ability, she gets name-smushed with a Marvel superhero. Spider-Lin, Wolverlin, etc.
At one point she even inherits her mother's nickname with "Iron Lin" after she puts on her metal armor in a way very similar to how Iron Man puts on his armor.
Similarly, reference to "Bat-Mako" due to the similarity between Mako and Batman's backstory and angst. Sometimes Lin becomes "Commissioner Beifong".
Honora: Zuko's as-yet-unnamed daughter. Also sometimes called Ursa due to bad Sokka jokes when 'Honora' gets captured in Fan Fiction.
After General Iroh showed his ability to be a major badass that can fly by bending fire from his feet, fans began naming him Iroh Man.
Howl: The White Lotus guard who appears briefly in the first episode and lets Korra and Naga out. Since no name was given, he was dubbed Howl, short for Hot Order-of-the-White-Lotus guard. Most fanwork places him in a Crack Ship with Korra, their Portmanteau Couple Name being Howrra
The Androids: Desna and Eska forobvious reasons. Also: the Water Twins, Water Brats, or Water Twits.
Eska specifically is sometimes called "Icezula."
Prior to their official name (The Red Lotus) being revealed, Zaheer's gang was (and to an extent, still is) called "the Anti-Team Avatar," "the Irregular Benders," and the "Four-Nation Army."
Individually, Zaheer is Windbag, P'Li is Sparky Sparky Boom Woman or less-polite variants thereof, and Ming-Hua and Ghazan's respective in-series nicknames of WaterArmLady and Lava Guy were anticipated by the fandom before they were actually used on the show.
Ultimate Alien Force: Used to distinguish post-timeskip continuity without having to say the names of both shows at once.
"The Halloween Trio": The three monster-themed aliens, Benmummy, Benvictor, and Benwolf, are called as such due to the fact that all three are based upon the Universal monster line-up.
Chip 'n Dale Rescue Rangers
Ever since Rhyme And Reason established these names, many fanfictions give Chip the last name "Maplewood" and Dale the last name "Oakmont". In fact, this is accepted as Fanon.
Some fans go as far as declaring "Chip" the nickname form of "Charles", which would mean that he'd share a first name with Monterey Jack's father.
Tammy from "Adventures In Squirrelsitting" is often given the surname "Chestnut". Her unnamed mom has been named June in a handful of fanfics as well.
However, there are even more names for Tammy's mom to be found in fanfics than last names for the family.
"The Rangerillion" gave new names matching its Tolkienesque High Fantasy style to staff members, canonical characters, original characters, fans, and some classic Disney characters. Due to the impact this story had on the fandom (a Real LifeMoment Of Awesome similar to the release of Of Mice And Mayhem, only that it took several months), some fans occasionally use these names in regular conversation, sometimes not even shying away from addressing people, fans in particular, but also staff members, by these names. Examples:
The device built by Gadget out of the Rangermobile and the Gyromobile in "The Case of the Cola Cult" is officially unnamed, as is the walking contraption with which Gadget attacks the other four in "To the Rescue". Fans baptized them Gyrotank and Battlesphere, respectively.
While the name of Gadget's father is established in canon (Geegaw Hackwrench), there has never been any consensus about the name of her mother whom every fanfic writer names and describes differently. Or about how the name of Gadget's Evil Doppelganger from "Gadget Goes Hawaiian" is spelled.
Codename: Kids Next Door
La Superagente 86: Numbuh 86, based on the Latin American name for Get Smart (also used to refer to Smart himself).
The Satanic Children from Down the Lane: Based on how they resemble Damien and demonic children in general.
Kooks: Numbuh Three or Kuki. Popular in KND fanfiction in 2005, might not be so much now.
Violin Girl: The violin-playing Demon Head character from "Courage in the Big Stinkin' City."
Our Heroine (OH): Daria Morgendorffer.
Amigas: Jane and Daria, since Jane often calls Daria her "amiga."
Doomed Stacy: Used in fanfiction for Stacy Rowe when bad things happen to her.
Schloss Morgendorffer: The Morgendorffer home.
Casa Lane: The Lane home.
Evil T(h)om: Nicknames for Tom Sloane, or more specifically, Die for Our Ship depictions of him. Usually spelled this way, parentheses and "h" included.
The Kiss: The Tom/Daria kiss, which is also seen by some fans as the Jump Ing The Shark moment for the series.
Manstopper Glasses: The eyeglasses Daria wears.
Saint Mack: Used in reference to Mack as a long-suffering Nice Guy, particularly regarding his relationship with Jodie.
The Sisters Morgendorffer: Daria and Quinn.
The Lost Summer: The summer between Daria's sophmore and junior years, which is never explicitly shown or mentioned on the show (unlike the summer between her junior and senior years, which is the subject of "Is It Fall Yet?").
Backgrounders: Those characters which appear in the background but are never made particularly important. Many of them have Fan Nicknames and Fanon personalities of their own, especially those with unique designs.
Tori Jericho: A particularly common fanon name for the popular girl talking with Sandi and Tiffany during "The Invitation."
Alternate 1985 Cinderella: Cinderella III: A Twist in Time. ProgressiveBoink.com's Mike Fireball calls the film by this nickname in reference to its plot's similarity to that of Back to the Future Part II.
Frollo's aptly fan-named black horse, Snowball, from The Hunchback of Notre Dame, which is an animators' nickname that the fans started using too.
The Main Pups: Lucky, Rolly, Cadpig, and Spot the Chicken in the 101 Dalmatians TV series.
The Trio: The above group, minus Spot.
Disney Movies, The Animated Disney Movies: Some people refuse to use the word "canon" to describe something that isn't linked together by continuity.
Disney Television Animation's history:
The Disney Afternoon Era: The period between 1985 and 1995.
The One Saturday Morning Era: The period between 1996 and early 2002.
The Modern Era: The period from mid-2002 to the present.
The Lion King fans have taken the liberty of nicknaming quite a few of the more unique background Outsider lionesses from the second film. Here's the list.
Maia, Marjani- Ma from the midquel.
Elsaba- Elsa from Frozen, due to her being voiced by Idina Menzel and her character's similarity to Elphaba.
DKCTV - A shorthand name used to refer to the series.
Lord Harry: An alternate title, used by Rareware fanboys who hate the show.
Dora the Explorer
Dora the Whora: Around 2010 or so, Nickelodeon attempted to reinvent Dora so that she aged along with her audience, which ultimately resulted in the character becoming an appearance-obsessed early-teenager who only explored shopping malls. The attempt was ultimately left on the cutting room floor, but it got enough press that the nickname was inevitable.
Doug's Only Movie: The Movie, which was titled Doug's 1st Movie but never got a sequel.
Ugly Twerp: Gyro Gearloose. SharanMcQuack refuses to call Gyro by his real name because she thinks Disney is trying to pass him off as a hero while making her favorite character, Launchpad, look like an incompetent idiot (even though he is a rather goofy character).
Ed Edd 'N Eddy
The Retro Van: The purple, and very 70's, van the Eds use as a hideout in the Junkyard.
Meg-bashing: The constant abuse that MegGriffin undergoes.
Rian/Ryan: Another name for New Brian
Foster's Home for Imaginary Friends
The Foster's Five: Mac, Bloo, Eduardo, Wilt and Coco.
The Trio: Brooklyn, Broadway, and Lexington.
Bipper: Bill Cipher when he took control of Dipper's body in "Sock Opera".
Green Lantern: The Animated Series
Sad Rage Zebra Bunny: Affectionate term used to describe Canon Foreigner Razer. Coined from an offhand fan comment that his armour and Facial Markings make him look like a cross between a bunny and a zebra. "Sad" and "Rage" are occasionally supplemented with other adjectives depending on the fan.
The Legion of Doom: The second Secret Society in Justice League Unlimited, based on their deliberate similarity (including the design of their secret headquarters) to the classic enemies of the Super Friends. One editor has heard that internal documents actually refer to the Society as the Legion of Doom, but can't put their finger on any references.
They flat-out mention it in the DVD commentaries for the final season that they essentially referred to the group as the Legion of Doom amongst themselves, but were asked by DC higher-ups to not use it in the show. Hence why the group isn't actually referred to at all by name in the show (apart from Luthor's dismissive comment about it being another version of the Secret Society, which Grodd waves off).
It's on the DVD box!
Brainthor: The entity formed by Brainiac merging with Lex Luthor in the second season finale of Justice League Unlimited. (Other favorites include "Lexiac" and "Luthoriac", some even differentiating between the two stages of the event.)
Mjolnir: Hawkgirl's mace. Named after Thor's hammer, though it looks more like a morning star.
Also, the "Big Honkin' Mace" or "BHM", after a line Joker used to describe it.
The "Deus ex Mace-ina", due to Hawkgirl's ability to destroy or effectively attack things with the mace that sometimes even guys like Superman can't smash because of magic.
The Little Three: Hawkgirl, Flash, and Green Lantern.
The Big Seven: during justice league unlimited when referring to the original seven members.
The Iron Giant
Hog Hug: Used by some fans to refer to Hogarth Hughes, thanks to one hilarious scene with Kent Mansley and the smashed BB gun.
Alex Sapphic/Background Lesbian: A recurring background character in Kim's high school that fit the stereotype of a Butch Lesbian. (However, her displayed romantic interests in Smashmouth, Prince Wally, Hirotaka and various boys around the school indicate that she'd more likely be bi or pan.)
Leslie Bean: Recurring high-school extra that appeared in Season Four, appearing to be the Background Lesbian's girlfriend.
The Girl In Blue: Another Recurring Extra at Middleton High School who caught the eye of fans. Several names have been suggested, like "Linda," "Violet," and, inexplicably, "Soup.". Some promotional material names her "Linda" and one episode gives her surname as Platt (or it might be the guy in front of her).
Zorpox is actually the name of an in-universe-fictional supervillain Ron dressed up as to infiltrate a villain trade show. It became a convenient handle for the Evil!Ron persona that was accidentally unleashed at the trade show, but is never used that way in canon.
Mane Six: collective term for the main characters.
Background Six/The Other Mane Six: collective term for the six most popular background ponies (see below), those usually being Derpy Hooves, Lyra Heartstrings, Octavia, Vinyl Scratch/DJ Pon-3, Bon Bon, and Doctor Whooves. Sometimes the Doctor's spot will be filled by Carrot-Top/Golden Harvest or Colgate/Minuette to keep the "all girls" theme. On rare occasions, Doctor's spot will be filled by Raindrops to have the 2:2:2 ratio of ponies complete. Other additional members that are often included are Berry Punch and Rose.
New Mane Six: Collective term for Discord, Coco Pommel, Spitfire, Cheese Sandwich, Seabreeze, and Silver Shill, each of whom gave a member of the central cast their key during the events of Season 4 and most of whom are ensemble darkhorses.
Pretty much every background pony has a fan nickname or a few (here's the helpful list). Some of the most notable ones are listed below.
Derpy Hooves: A grey-furred pegasus who appeared as a background character in the first episode wearing a dopey, cross-eyed expression on her face, and has gone on to make appearances in several other episodes, usually with Fish Eyes. In the second season she's a recurring background character in the vein of Where's Waldo, generally seen in every episode. Very popular with the fans. Also known as Ditzy Doo, which is a canonical name for an unidentified, scatterbrained pegasus who went north to retrieve the southern birds (and west the previous year) and partially endorsed by Lauren Faust.
In a rare instance of the fan nickname becoming canon, "Derpy" went from a fan nickname, to being used in the promotion of the December 2011 holiday special, to being used on an episode of the show in January 2012 (in an episode that also gave Derpy her first speaking appearance), then subsequently de-canonized after complaints from parents caused Hasbro to re-edit her scene to remove her name (as well as change her voice and mostly-underp her eyes). The outcry also resulted in her being conspicuously absent from Season 3 (except for the opening, which is a Season 2 holdover) though she reappeared in time for the season finale.
For the record, the writer of that episode had originally planned on using "Ditzy-Doo", but changed it at the last minute at the request of the director, who wanted to give a further Shout-Out to the fans.
Dr. Whoof/Dr. Whooves: An earth pony with an hourglass-shaped cutie mark and an uncanny resemblance to David Tennant who appears in a few episodes as a background character. Fans don't seem to have decided on a name.
According to his trading card, his name is officially Time Turner, and he deals with all things 'timey-wimey' in Ponyville. Also referred to as "Dr. Hooves" in the merchandise.
In one particular crowd scene, there were a few stallions who resembled various incarnations of the Doctor. All of them had the hourglass cutie mark, just to make the connection more obvious.
Aloe & Lotus, the Spa Twins: The proprietors of the Ponyville Day Spa, who are pallete-swaps of each other (and share the same cutie mark, a lotus blossom). Aloe is pink with a blue mane; Lotus is blue with a pink mane. One toy canonized the blue twin's name as "Lotus Blossom". A third spa pony – light tan with a purple mane – has been given the fan nickname "Vera".
Carrot Top: The yellow earth pony with orange mane and carrot cutie mark. Later canonized as Golden Harvest, but the fan nickname remained as an "official nickname" of sorts (it's mentioned on the back of her trading card).
Pony Gaga: Rarity in her Pimped-Out Dress and Uncanny Valley Makeup from "Sonic Rainboom". The nickname has also been used for Photo Finish from "Green Isn't Your Color", despite Photo Finish actually being modelled after Vogue editor Anna Wintour.
Steven Magnet: the camp sea serpent from the second episode, "Elements of Harmony". The nickname comes from a caption generated by Youtube's closed-caption auto-generator. Has eventually become Ascended Fanonthrough the toys◊.
Basil: the big red dragon from "Dragonshy", after a dragon with a similar character design from the G1 series.
The Plot: Used to refer to gratuitous shots of mares' hind-ends (a.k.a "pony-ass"), most famously Rarity's in "Dragonshy". Taken from the pre-existing fan phrase "I watch it for the plot".
Trollestia: Princess Celestia, in light of later season 1 episodes which have shown her to have a somewhat mischievous streak.
Octavia: the cello/double bassnote It looks more like a double bass, but Word of God says it's a cello; either way her cutie mark is technically incorrect, as cello parts are almost never written in treble clef player from the season 1 finale. The official trading card later canonized this name.
Vinyl Scratch/DJ P0N-3: The DJ unicorn with the neon mane and rose-tinted glasses who first appeared for five seconds in "Suited For Success", bobbing her head to the music she queued up for Rarity's first (failed) fashion show. The trading card, toy, and extended "Equestria Girls" promo all name her "DJ Pon-3", but the "Vinyl Scratch" name has been seen on booth art Hasbro has displayed at trade shows.
Lyra: The green unicorn with a lyre (small harp) cutie mark. Her initial blind bag release in Europe named her "Heartstrings", but her American brushable toy (as well as the trading card) added the fan nickname to make her canon name "Lyra Heartstrings".
She is often seen with Bon Bon, the tan pony with the purple-n'-pink mane and three-candies cutie mark. "Bon Bon" is itself a fan nicknamenote she's named after a similar-looking pony from the G1-era My Little Pony Tales cartoon. Interestingly, this pony is the only one of the 8 most popular background ponies to not have any canon name at all.
In the 4th run of the FiM Blindbags, there is a Crystal pony by the name of Sweetie Drops that shares Bon Bon's cutie mark (but Applejack's appearance for some reason). Whether this has been formally adopted as Bon Bon's canon name is unknown though. Furthermore, the second series of Enterplay trading cards gave Bon Bon her own card, and actually used the name "Bon Bon".
With the release of a brushable toy as part of the "Cutie Mark Magic" wave, it appears Sweetie Drops is now her canonical name.
Fleur-de-Lis: The tall, slender unicorn seen with Fancy Pants during "Sweet And Elite"note She uses the same body model as Luna, minus the wings. Also, her relationship to Fancy Pants is not made clear; she could be his wife, girlfriend, or mistress. The nickname refers to her cutie mark.
Cutie Mark Failure Insanity Syndrome (Generally referred to as CMFISy): Used to refer to whenever a member of the Mane Cast goes crazy, because whenever they go crazy, most of the time it's because their special talent is being somehow compromised.
Pinkie Pied Piper: Refers to Pinkie Pie using music to lead the Parasprites out of Ponyville in "Swarm of the Century".
Pinkamena Diane Pie: Pinkie Pie's full name. In the fandom, however, it is used almost exclusively to refer to her straight-haired depressed or psychotic self.
Liarjack: Applejack during the season 2 premiere, after Discord turns her into a liar.
Meanie/Stinkie/Grumpy Pie: Pinkie Pie during the season 2 premiere, after Discord turns her into an angry stick-in-the-mud.
Avaricity/Rarigreed: Rarity during the season 2 premiere, after Discord makes her a crazy mare obsessed with Tom (see below).
Flutterbitch/Fluttercruel: Fluttershy during the season 2 premiere, after Discord corrupts her into a snarky Jerk Ass. Can also be used (along with Assertiveshy) to describe "new Fluttershy" a.k.a her after attending Iron Will's seminar in "Putting Your Hoof Down".
Rainbow Brash/Rainbow Fink/Rainbow Flake/Traitor Dash: Rainbow Dash during the season 2 premiere, after Discord makes her a deserter.
Tom Dan: A rock that Rarity befriends in the season 2 premiere after Discord tricks her into believing its a diamond and makes her become overly selfish and have even more Super OCD. Canon name "Tom", but called "Dan" by fans after Part 1 (before Part 2 revealed its canon name) due to YouTube Auto-Captions.
Screwball: A wall-eyed (possibly due to Discord though) purple pony who first appeared in the season 2 premiere, with a baseball and screw as her Cutie Mark.
Drama Couch/Fainting Couch: Rarity's couch that she summons to fall on in Lesson Zero. Has made a few cameos in further episodes.
Dream Beauty Celestia: The large talking Celestia toy, referred to as thus because it is the same size as ponies from the G1 Dream Beauties subline.
Also sometimes known as "Hasbrolestia".
Also derogatorily called "Pinklestia", for obvious reasons. Granted, this name applies to every Celestia toy out there except for the Limited-Run white Talking Celestia.
Doctor Fantastic: Rarity's dad in "Sisterhooves Social", thanks again to Youtube's automatic captions. His resemblance to Tom Selleck as the title character of Magnum, P.I. also lead to fans calling him "Magnum".
Twilight Snapple/Psycho: Twilight Sparkle during "Lesson Zero", when she went insane over her obsession with friendship lessons.
Roid Rage: The tiny-winged, comically-muscular white pegasus stallion from "Hurricane Fluttershy" who keeps yelling "YEAH!". He's also known by a number of other nicknames, including Heavyweight, Big McLargehooves, Horsepower, and Snowflake. The show staff settled on "Snowflake" for a while after his introduction, thought in "Rainbow Falls" he's officially known as Bulk Biceps.
"Queen Cheeselegs" is starting to gain popularity as a mocking nickname for the villain of the Season 2 finale, Queen Chrysalis, due to the Swiss-cheese-like holes in her legs, wings, and mane. "Swissalis" also seems to be as popular, for reasons already explained.
"Sandwich Armor": The sandwich Twilight Sparkle uses to represent Shining Armor in a mock dialogue in "A Canterlot Wedding, Part 1".
Negasi: The bat-winged pegasi who pull Princess Luna's royal chariot in "Luna Eclipsed".
Twily: Twilight Sparkle as a filly, which generally induces Cuteness Overload. The name comes from her older brother Shining Armor's pet-name for her in "A Canterlot Wedding" and "The Crystal Empire".
Liquid Pride: a euphemism for Manly Tears shed amongst the Bronies during the show's more heartwarming moments. The name comes from Shining Armor's denying that he's shedding tears of joy at his little sister's Princess coronation.
Flutterscream: Fluttershy's attempt at screaming in "Green Isn't Your Color".
Spitty: An abbreviated nickname for Wonderbolt captain Spitfire.
King Sombrero: A play on the name of King Sombra, Big Bad of the season 3 premiere "The Crystal Empire". Before his name was revealed, he was known as "Lord Donut Steel" by fans who thought his character design looked too much like some teenage brony's over-the-top Original Character.
"Wife Thrower": Shining Armor, because of how he threw his wife to save the Crystal Empire.
Tia and Woona: Princesses Celestia and Luna, when depicted as fillies.
Woona often refers specifically to Season 1 Luna, especially her fan depiction as a sort of blue alicorn Fluttershy.
Brad/Dreamy Cutebottom: The then unknown blue-haired boy appearing in the trailer for My Little Pony Equestria Girls, who was eventually named Flash Sentry. The former name comes from Rarity's boyfriend in the infamous parody videos; the latter was suggested by writer Meghan McCarthy.
Pony Ball Z: The battle between Tirek and Twilight Sparkle.
Sunbutt/Moonbutt: Celestia and Luna, referring to their cutie marks. Just a brief search through fanwork comedies (or anything with Discord in it, which remarkably *don't* always overlap) is enough to find them.
Unipeg: A Winged Unicorn. Friendship Is Magic fans typically say "alicorn" (as do the show staff). Sometimes called a "Pegicorn".
Core 7: The G3's mane cast. Pinkie Pie, Rainbow Dash, Scootaloo, Cheerilee, Toola-Roola, Sweetie-Belle, Starsong
Original 6: The original six ponies from the first year of the series – Blossom, Bluebelle, Butterscotch, Cotton-Candy, Minty, and Snuzzle.
Princess Rinse 'N' Spit: An infamous bootleg pony that goes by the canon name of just "Pretty Pony". She's well-known for her large vaguely Horse-like teeth.
Nirvana Ponies: Pony toys not released in North America.
The Nightmare Before Christmas
Bone-Demon: Jack and any fan-made skeletons like him. Understood to be a sort of sub-species of either Undead or demon. Usually used in the camp that thinks Jack and Sally have kids by natural means.
Dr. Finkly: Dr. Finklestein, by his fans.
Jewel: Dr. Finklestein creation/wife seen at the end of the movie. While there's no evidence that Finklestein's "Be careful, my precious jewel!" is a reference to her name, the fans use it anyways.
Some fans have taken to calling Kowalski "Walski-chan" or "K."
Phineas and Ferb
Before Word of God actually revealed the Fireside Girls' real names, one fan gave them these names (their real names are in parenthesis):
Shelly: The curly brown-haired Fireside Girl (Milly).
Sandra: The straight dark-haired Asian Fireside Girl (Ginger).
Marie: The straight brown-haired Fireside Girl with the sleeveless uniform (Adyson).
Kimberly: The light-skinned, blonde Fireside Girl (Katie).
Noah: The fat kid in the orange shirt.
Ballpit Kid: The short dark-blonde kid who dresses in green. He is nicknamed for a scene in "No More Bunny Business" where Phineas and Ferb retrieve him from a ballpit (oddly enough, his colors were wrong in that particular shot).
The Dork Brothers: Irving and Albert
Doofenshmirtz's unnamed girlfriend from Chez Platypus (the redhead wearing purple that had the "evil" tattoo) is widely known as Melinda, at least among the RP community.
The Powerpuff Girls
Blossy for Blossom, Bubs for Bubbles, and Cuppo for Buttercup.
"The Ultimate Experience in Grueling Terror": The episode when they "reboot" into an Evil Dead game. Watch the credits of that movie all they way to the end and you'll figure out why.
Male PMS Incarnate has sometimes been used to refer to Matrix and his. . . emotional issues.
Megabob: when Megabyte was pretending to be Bob in season 4
The Recess Gang: The main six characters (T.J. Detweiler, Vince LaSalle, Ashley Spinelli, Gretchen Grundler, Mikey Blumberg, and Gus Griswald).
Isabella: The background student with black hair, a pink bow, and primarily wears pink. Named due to her resemblence to Isabella Garcia-Shapiro.
Big-Lipped Kid: A background kid with light brown hair wearing a yellow sweater and a purple shirt, usually drawn with larger lips than the rest of the students. Also known as Ken Walker.
The Lost Episodes: Season six, due to the season actually made up of leftover episodes from season five that hadn't aired yet.
"The Song of Champions": The song Singer Kid sings in "The Ratings Game" about how all the kids rated nines were champions at something.
Fat Boy - Muscle Man
Shark Face - That bizarre face that Rigby makes when turned to the front.
The Goth Kids had fan nicknames before their real names were revealed in "Goth Kids 3: Dawn of the Posers"
Michael: Curly Goth/Tall Goth/Evan
Pete: Red Goth/Hair Flip/Dylan
Ferkle: Kindergoth/Little Goth/Georgie
The official scripts even utilized "Tall Goth", "Hair Flip", and "Little Goth" as placeholders for the three boys, even in the script for Dawn of the Posers before Parker and Stone opted to name them. Gameplay footage for The Stick of Truth also uses "Hair Flip" for Pete.
A VERY early nickname for the 4 main characters as a whole were "The Scamps".
"The Meteor Shower Trilogy": Cat Orgy, Two Guys Naked in a Hot Tub, and Jewbilee, respectively.
Likewise, there's the "Mysterion Trilogy": Coon 2: Hindsight, Mysterion Rises and Coon vs. Coon and Friends.
Kenny's mother was given the name "Peggy" in some early fanfiction, while a later fan dubbed her "Carol" which spread and was confused as her canon name. Kenny's sister was also given the name "Karen" in a fanwork, however, this one became Ascended Fanon and was eventually used in the show.
One particular British fan had coined several descriptive nicknames for minor classmates, some of which got confused for canon along the way (even far after some canon names were revealed): "Melanie" (revealed in the show to be "Esther"), "Lockie" (Francis), "Ruby" (Sally/Powder), "Ribbons" (Milly), and "Carrot" (Connor).
Asian SpongeBob: SpongeBob's face in "The Algae's Always Greener" when Plankton (who switched lives with Mr. Krabs at the time) told him he was using too much sauce.
The Little Guy: The title character. 'The Little Yellow Menace' could work, too.
Techno Twins: The Twins, due to the techno beat that plays whenever they appear.
Smart Convict: An early fan nickname for Nicky, due to his crafty nature.
Compassionate Convict/Caretaker Convict: Nicknames that some fans had used for Ash, as his name was only in the script in his first appearance and not spoken until season 2.
Stiletto/Jacqueknife/Jackie Knife: Nicknames for the Distaff Counterpart of Jacknife that appeared in the season 3 premiere.
Jackid/Pocketknife: Jacknife's illegitimate son.
"Midd"/Hamad: The recurring middle-eastern inmate.
Mr. Monopoly: A nickname seen for Warden's father, due to his resemblance to Rich Uncle Pennybags, especially the original 1946 depiction.
Sym Bionic Titan
Baron McBitchface: Lance's Academy rival from the episode Shadows of Youth is often referred to as this.
"Little Dance": Kimmy's strip tease in the episode Lessons in Love.
LL or Little Lance: Lance's flashback self in Shadows of Youth and Shaman of Fear
Waldo: The "Save Sym-bionic Titan" admin was unknown for a (long)while, and thus was named Waldo, after the infamous Waldo from the old "Where's Waldo?" finds. After they found out later, he was still referred to as Waldo. His real name is Brian.
Mommy: Kristin, mostly by LL. Kimmy was mommy for a wee, during which time Kristin was referred to as "Nana".
The ever obvious "The goth chick" as well.
By a hair, Daddy Todd, but no one says it anymore. During the brief period where Todd and Kristin agreed to take care of LL together. It didn't last long. A lot of nicknames came around AFTER the shows cancellation, and thus a lot of this isn't canon happenings, just things that happened in the "official" Sym-Bionic Titan RP. Yes, that's right. There's an official one.
Team E-Scope: the alliance between Noah, Izzy and Eva during the TDI special, or those three as a group for whatever reason.
Zeke: Ezekiel. Eventually used on the show, but popular in the fandom long beforehand.
Feral Zeke, Zombie Zeke, Creepy Zeke, Zombiekiel: Him after his personality change in World Tour. Zellum (a portmanteau of Zeke and Gollum) is occasionally used as well, especially after the Lord of the Rings parody in the finale.
Clone Cody or Evil Alien Clone Cody (EACC for short) for the Cody-duplicate that appeared in The Ex-Files. Has gained Memetic Mutation for his tongue and Seme status, and is shipped with various other members of the cast.
Armor, Weapons, and Ships
Chaingun of Doom, Chaingun of Command: Rhinox's gun, from Transformers: Beast Wars, first appeared in the episode "Chain of Command", hence the second nickname. Later made canon in Transformers: The Ultimate Guide, and used again in Rhinox's 10th Anniversary toy re-release.
Hellbelcher: Rampage's huge gun, also from Beast Wars.
Megahead; Big Floating Head (BFH): The giant, head-shaped ship from the second season of Beast Machines.
Shows up again in War for Cybertron as a Soldier upgrade (P.O.K.E. Alpha, increases Whirlwind damage) and the Leader class's 5-killstreak reward (P.O.K.E. 2.0, a one-hit-kill melee attack that, when equipped, causes your team's announcer—either Optimus Prime or Megatron—to announce, "Punch of Kill Everything equipped!").
Megs: Megatron, from any given Transformers series. Was once applied canonically to Beast Wars Megatron, but has been used before and since in fandom circles.
Galvy: Most versions of Megatron from Transformers become Galvatron, hence picking up this nickname. Never used in canon.
The Stooges: Slapper, Dark Scream, and Gas Skunk, from Transformers: Robots In Disguise. The three of them are comic relief villains who are always seen together.
Optimus the Grey: His ability to come back better than before.
Screamer: Starscream, especially after hearing his voice.
Skywarp actually called him "Screamer" in the G1 episode Fire On the Mountain.
"Have a good time playing Crystal Nurse, Screamer. Byeeeee!"
Additionally, [Adjective Here]!Scream for the Starscream clones: Fem!Scream, Liar!Scream, Scared!Scream, etc.
The clones were also referred to by the name of the G1 character they resembled— Thundercracker for the blue one, Sunstorm for the yellow one, and so on. Unfortunately the female had no counterpart, so she was often referred to as Femmescream, Girlscream until her real name, Slipstream, was announced at Botcon.
Slipstream's name could be shortened to "Streamer", then the other clones could be "Warper" and "Stormer".
Other names for the Female Starscream were "Bitchscream"; "Dirge" (after another seeker); "Laserwave"; or "Susan".