Rock Megaphone brings us Lightradiantperfectebonyclawsonicflightdementiaechoserenitytarachime the Chimecho, shorted conveniently to "Chimey". She actually doesn't care what part of her name you call her, as long as it isn't "Lrpecsfdestc". The Chimecho race uses a naming system similar to that of Warrior Cats, and her parents just went a little... overboard. Because she has "ebony", "dementia", and "tara" in her name, that probably makes it a Shout-Out to My Immortal.
Toy Hammer gives us this little gem: 'Shas'ui Fi'rios Yon'anuk Eldi'myr', which is a Tau name can be condensed (from his language): Fire Sergeant Talon of Fi'rios (a colony). It is also hinted that Commander Firestrike's full name is much, much longer, considering that the Tau collect portions of their names from their achievements and traits rather than simply being named at birth.
At one point in Sith Academy, Darth Maul visits Dr. Lwkncalkdwoinvcalkdslaksowieuriuaoinclskdnfoaiwheoisldkhklgalskdhwoiazlzowx xvas-OOM! the 2983rd.
There is a Harry Potter OC that has so many different family alliances (mother, father, foster father, soulmates, etc) that the name her magical family tree recognized her as was "Elizabeth Grace Anastasia Malfoy-Moss-Flitwick-Flint-Lupin". Lampshaded by one of her friends with "Girl, make your mind up!".
Also, as a Shout-Out to the amazing Kendra Lucius Malfoy's full name was Lucius Dorian Archibald Marcus Nathaniel Malfoy.
What About Witch Queen? has it with Tamperan intel agency/police, called "Keisarillinen Vartiointipalvelut". The author notes that this are actual Finnish words, meaning literally "Imperial Secret Service". The second time he has to use the name, Madsen just says "KV".
Earth and Sky has Pinkie's daughter Tootselina Margaret Esmerelda Gummy Pie.
There's also Pipsqueak, whose full name is Peregrin Algernon Horatio Squeak.
In Alaia Skyhawk'sA Question Of... series from Merlin, the titular hero has a tendency to acquire additional names almost everywhere he goes. He eventually ends up with a list of names and titles longer than the king's. At last count it was Lord Merlin Emrys Ambrosius Stormcaller of House Garrah, The Last Dragonlord, Leader of the Storm Clan, Raeswa of the Druids, First Advisor to the King, Court Sorcerer of Camelot.
In Blessed Be Providence Harry is blood-adopted by Antonin Dolohov, who renames him Harrison Charles Antoninovich Delacroix Dolohov. When Voldemort says that it's a large name for such a small boy, Harry replies that "papa" always says he'll grow into it.
The Game of the Gods has a female named Juliardianselaáfalayu. Her name is so long that Fëanor invents a new script to write her name in only three letters.
MagnoliaCinderellaCupcake. The title is her full name. The story always uses her full name. There is no shorter form of her name, but there is copy and paste.
Middle Earth And How I Saved It has a main character named Siltasuvi Araeina Raven Tri'shah Iuhlmati Ellenor Isabella Geliarae Arwen Sarabelle Kitsune Hmrevenueandcustoms Smith.
In the deleted story UnSueing, some characters greet Phoenix by reciting her full name,
Phoenix Eternity Emilee Adriana Marie Hunter Ixia Ivory Pearl Opal Rose Lily Sunray Scarlet Ruby Garnet Flame Diamond Star Moon Destiny Shadowheart Firestar SausugeFire Tango Amethyst Diamond Shinning Shiny Potter Hope Wish Golden Gold Red Green Emerald Azure Emerald Sapphire Ruby Diamond Pearl Jade Topaz Opal Amber Hawaii 73938-03894-PIN-LAST-NAME-MALFUNCTION
The knights' Weird Trade Union in Warriors of the World sports the full name of "The Prontera Royal Chivalry of the Honoured Knights of the Kingdom of Rune-Midgard". No one refers to it by this name except on official documents, preferring to just call it "the Chivalry".
The titles of each story in The Vinyl And Octavia Series are all quite a mouthful. The one that takes the cake would have to be Vinyl and Octavia Machete Their Way Through The Jungle.
In Steps in Life one of Harry and Susan Bones' daughters is named Hermione Minerva Luna Amelia Sally Potter.
In The Horror! The Horror! the editor of the Daily Prophet is named Morton Throckmorton Aloysius Ottoman Pendergast Biedermeier Jones VIII.
In Long Awaited due to a number of unexpected inheritances Harry becomes Harry James Rhys Evan Potter-Black-Flamel-Gryffindor-Slytherin-Ravenclaw-Peverell.
In Movie Night At Freddy's, Freddy Fazbear's full name is revealed to be 'Frederick Ferdinand Floyd Franklin Finnegan Fraser Fazbear the Fifth'. Later, that name turns out to be a slightly less abridged version; the actual full name is Frederick Ferdinand Flavius Francisco Fitzwilliam Fleming Fremont Fitzroy Forrester Finley Floyd Franklin Finnegan Fiorello Fraser Fazbear the Fifth.
In the Harry Potter fanfic King Of Kings Ruling Over Rulers, due to the old tradition of royal families to stack up names, plus the old tradition of Eastern Roman dynasties to add the names of other prestigious families to their own, when Harry Potter was born (in a matrilineal marriage, therefore he lacks the Potter in his name despite being James's son), his full name became:
Hadrian Maria Alexander James Philip Charlus Manuel Michael Gabriel Raphael Francisco de Assis Eugenio Doukas Angelos Komnenos Palaiologos von Habsburg and Anemas.
In Sonic X: Dark Chaos, the Prophet Muhammad's full name is Muhammad Ali Hussein Abu al-Addin bin-Laden al-Zarqawdi Talib.