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.
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 was blood-adopted by Antonin Dolohov, who renamed him Harrison Charles Antoninovich Delacroix Dolohov. When Voldemort said that it was a large name for such a small boy, Harry replied that "papa" always said he'd grow into it.
The Game of the Gods has a female named JuliardianselaŠfalayu. Her name is so long that FŽanor 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 was named Hermione Minerva Luna Amelia Sally Potter.
In The Horror! The Horror! the editor of the Daily Prophet was named Morton Throckmorton Aloysius Ottoman Pendergast Biedermeier Jones VIII.
In Long Awaited due to a number of unexpected inheritances Harry became Harry James Rhys Evan Potter-Black-Flamel-Gryffindor-Slytherin-Ravenclaw-Peverell.