After "Gem Harvest" revealed that Greg's birth name was DeMayo, it's not uncommon to see "Steven DeMayo" used as a tag to refer to Steven himself. This includes variants such as Steven Quartz DeMayo and, after "A Single Pale Rose", Steven Diamond DeMayo. Became Hilarious in Hindsight as "Together Forever" revealed that Steven changed his full name to "Steven QuartzCutiepieDeMayoDiamond Universe".
The full-Gem version of Steven in "Change Your Mind" is generally agreed to be called "Pink Steven". This name is also used by some of the staff as well, but was not in the episode itself.
"Pink Steven" is also used to refer to Steven when he's using his new powers in Future.
In "Fragments", Steven gets a temporary redesign. He is taller, more muscular, and has a partial pompadour to reflect Pink Diamond's hairstyle. This version of Steven is called "Chad Steven", "King Diamond", "JoJo Steven", or "Steven Joestar".
In Future, Steven's giant monster form is called "Kaiju Steven" or "Stevenzilla".
Garnet:
is affectionately called "Square Mom" by fans, due to her square-shaped afro. Calling her "Mom Squared" also became popular after the airing of "Jail Break".
"Cotton Candy Garnet" is a fandom-wide term for Garnet's first form, due to her fluffy pink and light blue multicolored hair and general pastel color scheme. This name was referenced inUnleash the Light, where the first formation skin for Garnet's gauntlets is called "Cotton Candy Gauntlets".
Amethyst:
"X-methyst", with X being whatever Amethyst is shapeshifted as — the most common variation probably being "Owlmethyst" (which is actually an official term◊).
"Purple Grimace" is used for Amethyst's purple skin and odd facial expressions in the first season.
Unlike the other Gems, Amethyst has a variety of "Mom" nicknames, including "Purple Mom", "Grape Mom", or "Fun Mom". "Purple Mom" is the most commonly used.
Her name is often shortened to “Amy” or “Ame” as well.
It’s not uncommon to hear Amethyst referred to as “the purble” (a nod to a Flight Rising meme), for fairly obvious reasons.
Pearl:
Pearl is commonly referred to as "Bird Mom" due to her pointy nose.
In order to differentiate her from other Pearls, Pearl is sometimes called "CG Pearl" or "Our Pearl", the latter because the Gems sometimes refer to loved ones as "My/Our X".
Peridot:
is often called "Dorito Gem", "Lime Dorito", or "Peridorito" due to the shape and color of her hair.
After her Escape Pod fired off in the general direction of Ontario at the end of "Jail Break", she became known in some circles as "Canadot". The nickname died down when "Joy Ride" indicated that she landed near Beach City.
Peridot using her limb enhancer fingers as a makeshift helicopter is commonly referred to as "the Pericopter".
Upon the reveal in "Catch and Release" that her real body is actually quite short (barely taller than Steven), people started calling her "Smoldot", "Tinydot" and "Perismol". Steven comparing her to "an angry little slice of pie" inspired the nickname "Pieridot".
"Peridemption" is the term fans use when referring to Peridot's Heel–Face Turn.
Some fans, in the interest of keeping the "Mom" themed nicknames of the Crystal Gems, gave Peridot the nickname "Nerd Mom".
While most of Amethyst’s In-Universe nicknames for Peridot haven’t caught on in the fandom, one, “Peri,” is fairly popular.
Lapis Lazuli:
Inspired by the drawing Greg made of her in "The Message", Lapis is commonly referred to as "Water Witch". Substituting witch for another word, like "Mom" or "Angel", is also popular.
Fans refer to scenes of Lapis genuinely smiling or being happy as "Happy Lappy". In contrast, "Lapissed Lazuli" is used for scenes where Lapis is incredibly pissed.
Jasper:
is called "Big Buff Cheeto Puff" due to her orange skin and muscular build. Loving fans also like to call her their "Bara Cheeto Wife/Mom".
Jasper's Corrupted form is called a "moldy cheeto" due to her growing green spots all over her body. Due to her resemblance to a dog, "Jaspuppy" or "Jaspupper" is also quite common.
Mystery Girl:
In an example of a Production Nickname that caught on in the fandom, a lot of people refer to Mystery Girl as Sheena, due to Jessie Zuke saying that they called her that while designing her.
Since Kevin has an unseen ex-girlfriend named Sabina, a name extremely similar to Sheena, many have speculated that she and Mystery Girl are the same person and refer to her by that name accordingly.
Some fans jokingly call Mystery Girl "Punk Diamond", as a reference to her appearance being "Rose gone punk" and to the old "Rose is Pink Diamond" theory. Rose actually being Pink Diamond made the nickname all the more fitting.
The Diamonds' Pearls:
For the sake of differentiating them, fans refer to the Pearls by what Diamonds they serve: Yellow Diamond's is Yellow Pearl, Blue Diamond's is Blue Pearl, White Diamond's is White Pearl, and Pink Diamond's (who has the In-Universe Nickname "Volleyball") is Pink Pearl.
Yellow Pearl is called a lemon due to her hair. A certain smug facial expression in "Message Received" also led to her being dubbed "the Grinch".
Blue Pearl has been dubbed "Moppy" because of her flowy hairstyle that covers her eyes.
Upon her official reveal, fans started calling Bismuth "Rainbow Mom" or "Gummy Worm Mom", because of her dredlock-style multicolored hair.
Lars:
As of the "Wanted" block of episodes that comprise Season Five's premiere, fans have taken to calling Lars "Larzarus" after Steven brings him back from the dead.
Following Lars' revival, several fans have taken to calling him Pink Lars, due to his skin and hair turning pink. It's also sometimes used as an indication to which version of Lars a fan may be talking about, due to Lars' Character Development following his resurrection drastically shifting his personality.
A fairly widespread one that cropped up after "Lars of the Stars" is Captain Larslock, due to his attire and the general Space Pirate antics the Off Colors got up to on their way back to Earth.
Fluorite:
As a massive permafusion with a worm-like body and the demeanor of a kindly old lady, many fans were inspired to start calling her "Caterpillar Grandma".
"Polygrammarous", as a pun on Fluorite being a stable fusion of multiple Gems, comparable to a happy polyamorous relationship.
Spinel:
Before her name was revealed, a lot of people dubbed Spinel "Heartstone", due to her heart-shaped gem.
In line with the Crystal Gems' "Mom" nicknames and her child-like appearance and demeanor, some have started to call her "Noodle Child".
Mega Pearl:
Many fans prefer to call "Prince(ss) Pearl" because of her attire.
Due to her heavily being based onUtena and Anthy, Many fans love to call her "Utena Pearl". Less seriously, some people have also called her "Revolutionary Pearl Utena".
Everyone else:
Although it's not as common as the other Gems, Nephrite, specifically her semi-Corrupted form, is called "Bug Mom".
In reference to Peridot's Dorito nicknames, Sardonyx's triangular head and stylish costume makes her the "Tuxedo Dorito Mom" or "Dapper Dorito".
Jamie has been given the nickname "Drama Deliverer" because of his job as a mailman and aspirations of being an actor.
After her first appearance, many called Blue Diamond "Sith Diamond" to due her In the Hood attire and Big Bad vibes.
Yellow Diamond is referred to as a giraffe or "Giraffe Mom" due to her yellow color scheme and comically long neck.
As a nod to Jasper being the "Big Buff Cheeto Puff", fans have taken to calling Topaz "Big Thick/Thicc LEGO Brick" due to her square body shape, yellow skin tone, and cylindrical gems that resemble the studs on a Lego piece. "Big Yellow Marshmallow" is also common due to her loving personality.
Aquamarine is described as "The Evil Emoji Fairy", due to her fairy like appeareance and her gem placement (tear-shaped gem on her left cheek), making her somewhat resemble the infamous "crying laugh emoji".
Defense Zircon and Prosecuting Zircon are called Blue Zircon and Yellow Zircon by a majority of the fandom.
Before Defense Zircon's name was revealed, fans dubbed her "Moonstone" after seeing her crescent-shaped hairstyle.
Padparadscha is often known as "Paddy" or "Pads" for short.
Some of the "Famethyst" from the Zoo Station are popular enough to get names of their own, including Jay (8XJ), Sharky (with the super-pointy teeth), Chip (the burgundy one with a chipped tooth), and Carny (the only Carnelian in the whole bunch).
Fans refer to White Diamond as a "lightbulb" because of how brightly she shines.
Before her name was revealed, some fans called the unnamed Jade Fusion from "Together Alone" "Lemonlime", due to her components being a lemon-green Jade and a lime-green Jade. Her actual name is Lemon Jade, so fans weren't that far off.
The blocky-headed Jades at the Era 3 Ball are mockingly called "Thomas the Tank Engine Gems", since their headshapes and facial features resemble said train somewhat, in addition to their dressing resembling gears and how they dance around each other in a gear-like motion.
Steg (the fusion of Steven and Greg) has been given the nicknames "Mr. Multiverse" and "Greven", the former due to him being a fusion of two "Universes" and the latter being the other commutation of the portmanteau. The former was actually used in passing by Rebecca Sugar while discussing his concept art, implying it's his full name.
Bluebird Azurite is commonly referred to as a cockroach, a gremlin, a cockroach gremlin, and "(The) Cockroach Fusion", due to her personality, multiple legs, and small stature. The names gained more popularity and hilarity after her debut episode, where Alexandrite squashed her like a bug.
While the two do have Production Nicknames, the Lapis Lazuli duo introduced in "Why So Blue?" are more commonly known as Freckles (Nice Lapis) and Curly (Mean Lapis). Together, the two are "The Lazulis" or "Double Trouble".
Many, many people speculated that the huge creature in the background of Future's opening was a Corrupted Steven, with most calling it "Wormy Boi" due to the fact that it looked like a worm or caterpillar. It was also known as "Alaskan Bull Worm Steven/Alaskan Bull Steven" due to its resemblance to the eponymous giant pink worm. The theory was entirely correct, except the form had legs and was bipedal.
Other/Meta
Gems as a whole are often called "alien space rocks". The Crystal Gems, more specifically, will often get called "Queer/Gay/Lesbian space rocks/Alien waifu".
Back before it was revealed that they were part of the same song, the second part of "Love Like You" was called "Nothing Like You" by fans, due to the verse ending on that lyric and having a much bleaker tone compared to the first part.
The Summer of Steven/Steven's Summer Adventures event (where a new episode aired every day for a month) is called the Steven Nuke in reference to the Steven Bombs (where a new episode aired every day for a week); the term was later officially used by Ian-Jones Quartey to describe the event during San Diego Comic-Con 2016.
Some members of the fandom refer to Rebecca Sugar as "Sucrose", sometimes jokingly, sometimes as an insult.
Episodes that focus on Beach City citizens are commonly referred to as "Townie episodes".
"Lion 4: Alternate Ending" led to a rise in the use of Nora as a name for Rule 63 iterations of Steven, as opposed to the ostensibly-obvious Stephanie.
A theoretical Fusion between Padparadscha and a Ruby (most often Leggy) is sometimes jokingly called "Dumbnet" by fans, on the assumption that combining a Ruby's lack of intelligence with Padparadscha's Delayed Reactions would create a Garnet that isn't very bright.
Steven Universe: Future has been nicknamed Steven Universe: Shippuden, due to both being Sequel Series that tack on a random word to the end to separate itself from the previous series.
as well, but was not in the episode itself.
