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.
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.