Granddaddy - a nickname given by most modelers to the RX-78 Gundam, due to being the very first one to bear the name.
Ped Comet - Another name for Char due to his rumored questionable relations towards underaged UC girls like Lalah and Quess (Puru is often roped into this group due to Super Robot Wars series coexistence hijinks).
Gruntmobile - The GM, The Federation's mass produced mobile suit in the UC continuity.
Gundam 0081 - The nickname given to the latest UC Gundam videogame project before its official name was known. The game was eventually released under the title Mobile Suit Gundam Battlefield Record UC 0081.
No Zaku - The MS-07B Gouf, after Ramba Ral's memetic declaration to Amuro that it is "no Zaku, boy! No Zaku!"
Papsmere Circus - Paptimus Scirocco. The guy had such a silly name already, it just had to be made even sillier.
Banana Clips - Banagher Links of Mobile Suit Gundam Unicorn, due to his silly first name, yellow eyes, and the Unicorn using a magazine for its beam magnum (some magazines are called banana clips due to their shape).
Bikini Babe Assault team - the girls that attacked Uso Ewin's Gundam on Katejina's orders. In space. With RPG's. Wearing nothing but... well, guess.
The Red Comet Begins - a nickname to the upcoming animated version of Mobile Suit Gundam: The Origin, with the first episode covering flashbacks to Char and Sayla's childhood.
Last Shooting - the nickname for the famous scene in Mobile Suit Gundam where the RX-78, headless and one-armed, stops in a tunnel in A Baoa Qu, aims its Beam Rifle upwards and fires one last time as the Zeong does the same, striking down the legendary suit. Parodied and referenced to hell and back.
Char "Ago"nable/"Agoi Suisei" ("Chin Comet") - Derisive nicknames created by Japanese fans toward the live action depiction of Char in the little-known FMV game Gundam 0079: The War For Earth. Said nicknames stem from live action Char's rather prominent chin ("Agoi" means "chin" in Japanese, by the way.)
Student of the School of the Undefeated of the East - any character in any series (yes, even non-Gundam series) that does something suitably badass (i.e. manages to fight Humongous Mecha hand-to-hand, Nightmare of Nunnally!Zero and Alberto the Shockwave are the most notable) is often given this distinction (after Domon and Master Asia's reality-warping martial art feats).
The After Colony Era
The Perfect Soldier - Heero Yuy
The Bat-Gundam - The Deathscythe Hell, especially the Endless Waltz version, because of its resemblance to Batman.
The Leo mobile suits became quickly known as "TV Heads" because their large flat head monitors looked more like TV screens than an eye camera.
"Ghibli Gundam" for the series as a whole. The scenery is full of Ghibli Hills, there are a lot of airships and antique planes early in the show, and the kind, pacifistic protagonist coupled with the overall hopeful and idealistic themes are probably what you would get if Studio Ghibli ever did their own Humongous Mecha show.
The Druggies - Orga, Shani, and Clotho, the three Alliance Gundam pilots from late in the series; they can fight on the same level as genetically enhanced Coordinators, but require a special drug (with horrible withdrawal symptoms) to do so. Notable for being used as more of a term of affection than derision among the fandom, despite the name's negative connotations. The Japanese equivalent of this nickname is "Baka Trio", from the word for stupid or idiot.
The Japanese fans also refer to Sting, Stella, and Auel (the Alliance Gundam pilots from Destiny) as the New Baka Trio; American fans never really gave them a nickname.
In the wake of his death, Chairman Durandal acquired the nickname "Space Commie Naraku" due to his striking resemblance to the Big Bad of Inuyasha and the fact that the Destiny Plan is essentially Communism IN SPACE.
Bad/Evil Amuro - Ribbons Almark, Alejandro Corner's useful and traitorous servant, as a result of being voiced by Toru Furuya, who played Amuro Ray from the original Mobile Suit Gundam, and there's also "Fucking Ribbons" after he reveals himself to be the true big bad and leaves Corner to die as well as many other bastard moves he does henceforth..
Prince Ali - Ali Al-Saachez, since his first name is a popular name for Arabian Nights princes, but most infamously the disguise used by Aladdin in the Disney version: Prince Ali. Thus, there has been some Memetic Mutation replacing Aladdin in his Prince guise with Ali Al-Saachez' face, and they even poke fun with his Image Song: "Prince Ali, Mighty Is He!"
Since his death, people have rewritten the meme to "Prince Ali, Mighty Was He." Rest in peace, O lovable bastard.
Johann Trinity, the eldest of the Gundam Thrones, is referred to as "Captain Hotpants" for being the leader of the trio and wearing very tight white shorts.
Setsuna F Seiei has...
Jihad-kun - particularly after his history with the terrorist organization KPSA was revealed.
King Arthur - Saji Crossroad, according to Soul Bro Ryu of the Gundamn! podcast.
Papa Bear - Sergei Smirnov, due to his in-series nickname "Wild Bear of Russia". Sometimes called 'Pedo Bear' due to his interactions with teenaged Super Soldier Soma Peries... even though his feelings were obviously fatherly.
After he dies, the nickname 'Pedo Bear' is inherited to his now much-reviled son Andrei Smirnov for the latter's affection towards a younger Louise Halevy.
Lecherous Lyle - after events in episodes 3 and 4 in season 2.
Doublelujah - (H)Allelujah, due to both personalities being active at once during (H)Alle's Moment of Awesome in the first season's finale.
The Red Ranger - Anew Returner. When the CB members got color-coded outfits in 00 season 2, fans wondered where the "red ranger" was. One eventually showed up. However it was Soma Peries/Mary Parfacy who dons a Red pilot suit and mecha in batttle.
The A-LAWS are less affectionately called as the A-HOLES by fans.
Also known as A-LOLS.
The name 'Bushido Bob' was given to Graham Aker in the mid-series break due to the mask he was seen wearing in the previews for season 2. The authors thought it was either cool or funny because he returned with the name of 'Mr Bushido', with the note "That's what they decided to call me." (It's all your fault!)
And because his new mechas, the Masurao, later upgraded to Susanowo, can use the Trans-Am system, it's jokingly called the Trans-GrahAm by fans. (Or more affectionately Trans-GARHam.)
One fan-dub of The Movie even uses this when he activates it to help Setsuna against the ELS blocking the way.
Some less affectionate fans call him "Flag fucker" for his... overly affectionate treatment of the various mecha (mostly Exia).
Speaking of his Flags, his last two mechs in season two have been called Shin Musha Flags due to their Samurai-based design.
And among those less than fond of his S2 image change described above he's known as "Mr. Bullshito".
Other fans have also called him Graham Crackers◊ due to the letters of his surname fitting in the second word.
Billy Katagiri gained the nickname "Zetsubou Billy" after Setsuna outed Sumeragi as a Celestial Being operative in front of him.
GN Guncannon - The "Reborns Cannon" portion of Ribbons' "Reborns Gundam".
Colonel Fatass - nickname given to Arthur Goodman, the fat A-LAWS commander.
An alternative is 'Captain KFC'.
According to the commentary from Ep 1 of Season 2, the crew referred to him as "Baker-San" after a comment by one of the cast.
The ESF president from season 2 was given the nickname "00bama", for looking very similar.
SoMarie - Soma Peries / Marie Parfacy, a portmanteau nickname.
Darth Louise - Louise Halevy in season 2, due to having a Red Right Hand (well... left hand in her case, but still) quantum brainwaves, mostly answering only to Ribbons, and other similarities between her and Lord Vader.
Gundam DD - The entire series in a whole, due to having many busty women.
Nena 2 - Meena Carmine, for having her name remain unrevealed for serveral months and for being Nena's Identical Stranger.
Corner's Counterattack - The hilarious film within a film shown at the beginning of Gundam 00: A Wakening of the Trailblazer. The fact that the asteroid base shown bears an uncanny resemblance to Axis does not help.
China Bitch - Wang Liu Mei, the Chinese Smug Snake who was quite unpleasant and whose attitude throughout the series was "I want the world to change, but I don't care who does it." Occasionally called China Tits because, like almost every other female in the series, she was large-breasted.
Nu Exia - The 00 QAN[T], due to its asymmetrical design, right down to the "funnels".
By extension, the 00 Qan[T] Full Saber gains the nickname "Hi-Nu Exia".
The Qan[T] is also given the nickname "telephone" or "glorified telephone" because of its in-series role as a conduit for Setsuna to communicate with the ELS.
Hank Hercules - Pang Hercury; this was the translation that at least one fansub used, and it stuck around for a while due to being a prime example of Awesome Mc Coolname.
Zabudget - Gundam Zabanya, because based on its sheer number of remote weapons, fans think that all of Celestial Being's budget went towards designing and creating it.
And instead of the "Final Battle variant", fans call it the "Final Paycheck variant", continuing the theme.
The Advanced Generation
Mega Man - Flit Asuno, based on the design of his pilot suit.
Cult of Graham - the sinister guys in black robes that appear in Ep.5, as their leader wears a mask almost identical to one worn by Graham Aker (during his stint as Mr. Bushido) in 00 S2.
GM Unicorn for the Genoace Custom, due to being a cross between Gundam Unicorn and a GM.
Gundam RAGE for the series itself, referencing the incredibly negative reaction to the series' announcement by many fans.
Super Pirate: Captain Ash of the Bisidian pirates, because he's a pirate and Asemu Asuno.
Kira Asuno/Kio Yamato: Kio, after adopting Kira's anti-killing mentality.
Also "tree-hugger" for his naivete that ends up getting a lot of characters killed.
Flit's worsening attitude towards the Vagans over Asemu and Kio's arcs has earned him the title Flitler.
And/or Grandpa Genocide in the Kio Arc.
Fans have dubbed "Flitoshiki"◊ an edited version of Flit's statue at the end of the series, complete with the kanji symbol "100" - supposedly a Shout-Out to the MSN-0100 Hyaku-Shiki from Zeta
Gundam Build Fighters
Gundam Boy Friends, since the show's title abbreviates to BF. Then there's the fact that there are abundance of shipping material, both the Ho Yay and straight variety.
Sazaki is often called Gyandere, due to his obsession with Sei and his preference of Gunpla.
Rinko is called Mama-n, the suffix ~n is used in Japan as to point out cuteness aloud.
Also it sounds the same like the Japanese slang Maman, who is the equivalent there of the phrase MILF.
The moment Sengoku Astray appeared fully as a model kit, it quickly earned the title Weeaboo Astray, having an overt Japanophile influence all around - even the name Gundam is written in Kanji.
The alliance of pilots who attack Fellini in episode 11 was quickly dubbed "Team NTR", since their entire motivation was revenge for Fellini stealing their girlfriends (though he insists that they came on to him).
Rainer is known as "Butt-hurt NTR guy" in Japan. Oh, and he lost the qualifier too.
This Ship Tease between Reiji and Aila has been named by reddit as "The Meatbun Chronicles". This has in turn lead to Reiji and Aila being referred to as "Mr. and Mrs. Meatbun".
"Gundam Valhalla", referring to the fact that Episode 23 showed off a bunch of cameos featuring a number of fallen or hard-lucked Gundam characters. Even the director has stated that this is pretty much where they all go to when they die.
From Build Fighters Try, it did not take long for an all under-water fighter team, consisting of three guys who dress only in speedos, to be nicknamed "Team Free!"
Later changed to "Team Free(ze)" after they were eliminated due to the Antarctic icecap being the battlefield.
The REAL Gundam Jesus: Meijin Kawaguchi III, who makes his official debut in Try by descending from the heavens in the Amazing Red Warrior, the sun silhouetting behind it and its arms spread outward, all while his Leitmotif which offly resembles a semi-Aramaic chant, plays in the background. It even emits particles that bring dead, withered plants back to life, and the final shot of the Amazing Red Warrior has the sun behind its head as a Background Halo. Unlike Kira's nickname, this is not intended as derogatory.
Jewhime/Jewfu: a nickname given by 4chan user to Kudelia Aina Bernstein of Mobile Suit Gundam: Iron-Blooded Orphans, due to her very old German/Jewish last name. What's more surprising is that it seems to be used adoringly, rather than in conjunction with racist stereotypes. Posters will often sing Kudelia's praises using Yiddish phrases.
Alternately, KOODELIAAAAA AAAAAINAAAAAA BAAAAAANSTEIIIIIN for Ein's Freak OutSay My Name incident near the end of the first season.
Hitlerstache guy: for Todo Mirconen, a member of the old CGS administration, who has a toothbrush mustache and is something of a jerk.
Space Guts: You can probably guess that this was Akihiro Altland's nickname from his very introduction.
In conjunction with the abovementioned, Gutsion for the Gundam Gusion Rebake.
There's also McGillis, who turns himself into McGriffith. Apart from his most infamous nickname below.
Chocolate Man: Mika has given McGillis Fareed an in-universe nickname that has stuck around since then. Due to his looks and role in the story, the portmanteau CHARcolate has also been popular.
"17-Year-Old" for Carta Issue, thanks to being cast byKikuko Inoue. Alternatively "Kabuki Lady", prior to her introduction, for looking like an actress in a Kabuki play; or "Kitsune Lady" for having fox-like features on her hair. Fanart of her with fox ears are aplenty, as a result.
Mikazuki "Punished" Augus in light of the fact that his right arm and right eye have been badly handicapped during the first season's final battle, adding on to the already numerous jokes that Orga is Big Boss and Tekkadan is Diamond Dogs IN SPACE!
On the merchandise side, a HG 1/144 heavily-armed red variant of the Gundam Astaroth was erroneously tagged as being from Gundam Build Fighters instead, leading to the nickname "Amazing Red Barbatos" (since it looked like it could belong to Meijin Kawaguchi III).
Ayame was given the nickname "Ninja Waifu" or even Adult!Akatsuki after her full appearance in episode 5.
Yukio's GM III Beam Master was given the nickname "Cheesemaster" due to its virtually-all-orange look.
Ogre's GP-Rasetsu was given the nickname "Getter Robo Gundam" or even just "Getter Gundam" as its head is strikingly similar to the titular robot, especially Shin Getter-1.
Said nickname turned out to be funnier as in a Super Robot Wars 4koma series, the Getter Team is trying to figure out what does the G in Getter Robo G stands for. They finally settled on "Getter Robo Gundam" in front of an unimpressed Bright Noa.
Wavehawking: Making a custom Gunpla, only for Bandai to announce that they are making a commercial version of the mobile suit in question. Named after an animesuki.com forum member called Wavehawk whom this happened to repeatedly.
Jean-Claude Gun-Damme: A model kit that can do full splits, with the HG 00 Gundam and Gundam Barbatos kits being notable examples.
Toothpicks: Beam saber parts in older kits, which tend to be molded in just one color.