Hawkward— Used to describe those moments where Rachel and Tobias are making the kissy-face/kissy-beak at each other.
KASU—Short for Katherine Applegate Screw Up and used to refer to the inconsistencies between books made by either the author or her ghostwriters. For example, Jake using thought-speak as a human in book one.
The titular character herself is sometimes called Anita Blake, Vampire Humper. Not by actual fans, generally.
The anti-fan/angry-fan nickname for her is 'mon petite fissure de ruine', which roughly translates as 'my little crack of doom'. (If you put it in an automatic translator... it doesn't really mean much in reality)
Lest we forget, 'Anita Blake, Village Bus'- because everyone has a ride at the same time.
Bitchard: used for Richard post-Narcissus in Chains when he goes from a naive love interest to a petty, jealous bastard.
The Emerald Witch, or The Green Witch - The Queen of Underland who kidnaps Rilian in The Silver Chair, since "The Lady of the Green Kirtle" doesn't sound evil enough. (At least one paperback edition's back-cover blurb calls her The Emerald Witch.)
To be fair, "Lady of the Green Kirtle" was what she called herself while she was still feigning benevolence. It wasn't supposed to sound evil.
Rinso - Rincewind, used a couple of times in The Last Continent.
Big Name Fans Stephen Briggs and Bernard Pearson are known as CMOT Briggs (after Dibbler, because he sells merchandise) and The Cunning Artificer (after the Street of Cunning Artificers, because he makes models and other Discly items). The former is almost official, since Briggs's merch website is called CMOT Dibbler, the latter has become very official with the opening of The Cunning Artificer's Discworld Emporium.
Zero!Rider (Iskandar) is called 'Ganondorf' for being a large swarthy redhead. He's also received the nickname 'Broskander the Great' for being Waver's awesome mentor.
Team Murdermoe - Caster and Ryuunosuke, as they are one of the very few Servant-Master teams to have a trusting, mutually supportive relationship with one another bordering on a Moe Couplet - and are both gleeful serial killers.
Franken-Gregor, Gregorstein, Qyborg or Gregolem, for the thing which Qyburn is making out of the deceased Gregor Clegane.
Un-Cat, for Lady Stoneheart, who is Catelyn Stark resurrected.
Not a spoiler: Gregor Clegane, the Mountain that Rides, is known in some fandom circles as the "Mountain that Rapes". Take a wild guess why.
Some fans also refer to George R. R. Martin (the series' author) as "The Mountain that Writes" due to his considerable girth. Others refer to him as "The Mountain That Doesn't Write" for the long gaps between books.
The "Weirwood Wide Web" for the magical network of knowledge and memories that unites weirwood trees.
The Purple Wedding is sometimes used to refer to Joffrey's catastrophic wedding, named after another even more catastrophic wedding that shortly preceded it. "Purple" supposedly comes from the color of the murder weapon, or perhaps the shade his face turns as he chokes to death.
The episode of show that Joffery's wedding happens during is even called by the fan nickname.
Conversely, the forced wedding of Tyrion and Sansa is sometimes known as the White or Golden Wedding because, while sad, at least nobody dies.
Fans of Stannis Baratheon (a lot of the fandom) call him Stannis the Mannis or Stan the Man.
Voldy, Voldypants, Moldywarts, Moldyshorts, Voldilocks - Voldemort, of Harry Potter fame/infamy. In Deathly Hallows, Peeves the Poltergeist actually uses the first, and Moldyshorts came from a parody sketch on All That.
Vapormort is used to refer to Voldemort when he was "less than a ghost". Quirrellmort is Quirrell possessed by Voldemort.
Ginny Jo Sue - the Ginny seen in books 5, 6 and 7, after she underwent a rather dramatic change of character that led to accusations by some of her being a Mary Sue. She is also known as Sassy!Ginny or Ginny II. Anti-fans who dislike the character may refer to her as "Gin-bot," "Gin-slut," "Snogdoll" or, interestingly, "Jenny" (after a typo in a German news article)
Worthless Canon Brats - Teddy Lupin and the respective Potter, Weasley and Malfoy children who appear in the epilogue. For obvious reasons, used by people who hated the epilogue and/or the canon ships.
Wotters: A more favorable name for the various Next Gen kids in the Weasley family. A combination, obviously, of "Weasley" and "Potter" (for Harry and Ginny's kids).
Moonstruck: Harry/Lupin fanfics.
Puppy Love for Sirius/Lupin fanics
Wotcher Wolfie for Lupin/Tonks
Gin and Tonic for Ginny/Tom Riddle
The Government Stole My Toad for Luna/Neville
Guns 'n' Handcuffs for Harry/Draco
Orange Crush for Harry/Ginny
Harmony or Pumpkin Pie for Harry/Hermione, the latter based on a fanfic where they kiss and Hermione notes that Harry tastes of pumpkin pie.
Fire and Ice for Draco/Ginny
The Good Ship for Ron/Hermione
House Sparklypoo - The fifth House where Mary Sues belong. Showed up in a one-shot Fan Web Comic and the name stuck. On Livejournal, user Pottersues came up with three more Houses for different types of Sue: Bitchiwitch (Jerk Sue), Tootsitramp (slutty Sue) and Qanonreip (Sues that ignore Canon depictions of character, and often add random elements from other fantasy series - "ooh, it's Professor Legolas, isn't he cute!").
See also the Harry Potter Summer, aka the summer of 2007, when both Deathly Hallows and the film of Order of the Phoenix were released within two weeks of each other.
Harmonians (or Harmoanians): derogatory term for Harry/Hermione shippers, anecdotally the most unhinged people/designated whipping boys in the fandom. Certainly only the more radical shippers would keep going past getting Jossed, and the author of The Girl Who Lived is claimed to be one.
The stereotypical hardcore Harmonian is defined by the following traits. They believe the series was ruined because Harry and Hermione didn't end up together. They think Hermione is too good for that dumbass Ron, engendering the hatred of Ron fans everywhere. They don't think Harry is quite good enough for that perfect goddess Hermione either, but he's the closest anyone could come since he's The Hero. They believe that Harry and Hermione's love so purely transcends base lust that it is evidenced by the very lack of any evidence. It's frequently assumed that Harmonians are either misguided feminists who see themselves as Hermione (if female) or fanboys who want to get in Emma Watson's pants (if male).
McGoogles/Preacher McGongle for McGonagall, Dumbly, Voldemint, Snap, Loopin, Serious Blak etc. - all from My Immortal
The Yule Brawl for the giant fight in Book IV after the Yule Ball, for the pun.
The pimp cane: The snake-headed walking stick used by Lucius Malfoy in the movies (it's never been mentioned in the books).
It's also called Snakey.
Pink Power Granger: Hermione as seen in the third film, in which she wore a pink hoodie during the climax.
The "blood quill": The bloodletting quill (a quill, that doesn't use normal ink, but the writer's own blood as an ink-replacement. The text written with this quill also appears in form of scars on the back of the writer's hand) which Umbridge forces Harry to write "I must not tell lies" with in the fifth book, due to the lack of any canon name. An associated Fanon theory states, that blood quills are illegal Dark Magic items and that Umbridge purchased hers from Knockturn Alley or another shady place.
The Scottish Book: Refers to Rowling mentioning that she might publish an "encyclopaedia" of the Potter universe, including information that didn't fit in to the books. Now looks less likely with the advent of the Pottermore website.
The First Wizarding War and the Second Wizarding War: The wars against Voldemort, again due to the lack of canon names. The First Wizarding War is the war which occurred in the Back Story and ended when Voldemort failed to kill Harry as a baby. The Second Wizarding War is the war which occurs during the series, starting in Goblet of Fire and ending in Deathly Hallows. Often Wiz War 1/2.
Sometimes also known as Vold War I and Vold War II.
After the release of the final film, Professor McBadass has become quite popular for Professor McGonagall.
Slytherfen: derogatory term for fans who think the Slytherins aren't as bad as the narrative voice paints them.
There's also "Snapefen" for fans who are excessively devoted to Snape and paint him as the most important and/or worthwhile character in the series.
Nicky, Nicolae [insert mountain here] - Nicolae Carpathia
Cam-Cam - Cameron "Buck" Williams, movie version
Stoney - Jonathan Stonagal
Ellenjay - the aggregate nickname for series authors Tim LaHaye and Jerry B. Jenkins, after their initials.
Meta-[character]: in Slacktivist, an Alternate Character Interpretation or deconstruction of a character, if said character displayed the kind of human emotions and reactions that are conspicuously absent in the series. For example, Meta-Chloe.
Doltboy - Marius, for being oblivious to everything beyond his love life and La Résistance, particularly the advancements of the Veronica in a Love Triangle he doesn't even know he's involved in. Note that "Doltboy" does not imply malice, it's more affectionate than anything else. May possibly originate from Javert referring to him as a "dolt of a lawyer" in the book.
Snookums - Inspector Javert. Comes from fans thinking up a reason why he only goes by his last name, and thus making up an embarrassing first name.
Fearless Leader - Enjolras, the resistance leader. Also "Captain Vest," for his signature outfit, and "Apollo," to whom he is compared in the book. Some also use Enjy affectionately.
R - Grantaire, one of the revolutionaries, who always signs his name with a "Grand R." Get it?
"Ponine" and "Zelma" for Eponine and Azelma are used by Cosette in the book. Ponine, in particular, has become popular in fandom. (Probably because Azelma doesn't make it in to the musical.)
The Brick - Affectionate nickname for the book itself, in reference to its size and weight.
Marjolras - The version of Marius depicted in several film adaptations, in which he, rather than Enjolras, is the leader of the revolutionaries.
Barricade Boys or Frenchboys - The revolutionaries, collectively.
Boyscout Spruce (Pioneer Yolochkin) - Rupert vok Felsenburg (Pioneer\Scout part is mostly based on the Soviet slogan "The Pioneer is an example for all the kids!", because Rupert was bluntly designed by author as the "Anti-Oakdell". Spurce trees are on the Felsenburgs' crest)
Broody-kun (rus. Unyl-kun) - Robert Epine (guess, why)
Diseased Old Man (Stariy bol'noi chelovek), DOM - Stanzler
Colonel Pest (Polkovnik Zaraza), Super-Valya, Octopussy - Valentine Pridd
The third and fourth series have the nicknames "Teapot" (From "tPoT" or "the Power of Three") and "Oats" (Slightly modified "OotS" or "Omen of the Stars").
A few charcters are occasionally referred to by their name prefix with a "y" on the end (Crowfeather/Crowy, Leafpool/Leafy, Ashfur/Ashy). Exceptions include charcters without Clan names, or names that sound too awkward like this (Sol, Brambleclaw, Jayfeather, Cinderpelt/heart), and Hawkfrost, where the "y" becomes an "eh" or "3h" for some reason.
Even some of the charcters who don't fit with this convention have their own nicknames. Brambleclaw may also be referred to as "Brambs" or "Brammie" and Jayfeather as "Jay-Jay".
The first four books are generally called the Rogue Squadron books, because that's who they're about. The next three, similarly, are called the Wraith Squadron books. It helps that the very first book is officially titled Star Wars: X-Wing: Rogue Squadron and the fifth one is Star Wars: X-Wing: Wraith Squadron.
It is also used as a particularly immature joke by his internet-dwelling detractors.
MWW - Mad Wizard Weber, aka David Weber, from his occasionally serving as a Game Master, before becoming a famous author. On his official forums, he's known as "RFC", since he actually posts on said forums under the username "runsforcelery".
Pterry - Terry Pratchett, based on Djelibeybian names such as Ptraci. Also The Man, after the description of A-M democracy ("One Man, One Vote; the Patrician was The Man, he had The Vote") and the OFiaH, short for Old Fart in a Hat, a description he applied to himself as the reason why a couple of kids wouldn't listen to him about how to play Doom. And consequently died.
Lately Pterry has taken to referring to his case of early-onset Alzheimer's as The Embuggerance, mainly to emphasize that it's not yet debilitating.
Neil Gaiman, who co-wrote Good Omens with Pratchett, is affectionately referred to as Gneil by many fans.
The Erins - The four authors who write the Warriors and Seekers series under the pen name "Erin Hunter". Each one is "an Erin", but will more often be referred to by their first name.
John Green is referred to by jgreen, j scribble, john green the dad, or pizzajohn.
Maureen Johnson is known as MJ, or Queen of the Jars.