Himuri: LOVES cat themed stuff. From cups, to socks and slippers. xD
Sakari: Even though in his case having his hair cut short and hidden under the hat would be logical solution to some of his problems, he just likes hawing his hair longer. Also pierced his ears many many times.
Kiyomi: She feels uncomfortable wearing long pants. She can wear dresses, but anything that covers her whole legs is a nope. Also she always carries snacks with her, because her stomach is a black hole.
IMMA BE HONEST i donno if these are quirky or just normal, i just wanted an excuse to blab about my characters 
Oliver: huge into the beatles, he'll use songs with some wordplay, this actually agitates Jr (cant show in the actual comic cause lyrics are what nails you). He also picky about his kitchen, dont move anything around, it'll drive him mad, he even has a baby gate to keep Jr out of there when hes cooking. Olie also has an issue with spelling, which is the reason he spells his short form "Olie" instead of "Ollie". this is also the main reason his brother spells his name "Jr" instead of "Junior" this was done when they were little and it just became the norm for both of them
Jr: he'll take a shower but HEAVEN FORBID HE TAKES A BATH (aquaphobia does that to a person). he tries to remember spells but always fails, he is too dependent on his magic he prefers vehicles that are a manual transmission (Stick), along with that, despite the license for a hovering/flying transportation device being way less expensive than a driver's license, he prefers to keep his feet on the ground and opted out for the ladder.
Both the brothers have a faint Liverpudlian accent, it definitely comes out when they get mad or flustered, this however is hard to portray in the comics
Lane: the new guy he can actually skim through a book with ease and at a rapid pace, this is due to him being dependent on spell books when it comes to special spells (the opposite to Jr). because he is a guardian to a younger sibling, he has a tendency to be kind of overbearing, this includes his friends. has hemophilia, will flinch even at red food colouring. BUT despite this, his energy attacks (the standard attacks he can do without a spell) are all SLICING attacks, the irony
I had to think about this for a bit, but some other people's answers reminded me of a few.
Black Robin:
Zephaniah- When he's uncomfortable, he tends to cover the side of his neck with his hand as if protecting it. This is because he was raised to never let anyone see his birthmark that is there. It's usually covered, but the instinct to hide it more is present when he gets nervous or upset.
Finny- He's like that one guy who read too many romance novels and strives to out romance even the corniest characters from them. Not exactly a flirt, but very flirty.
Tara- Sometimes says things that make her seem beyond crazy to the other characters.
RomaMates:
Satoshi- Doesn't quite understand emotions/social cues as well as most. His whole life revolves around experiments and research. Even his dating past was just to test what his sexuality was. He also has a habit of slipping between really formal and semi-relaxed forms of talking.
Dewi- His complete control of his appearance means he's only able to blush when he wants to, but those who know him well enough know that the tips of his hair will change colors with his mood sometimes. So he kind of does blush at times.
Blake- He's actually a really flirty guy that enjoys doing crazy things, but his anxiety gets in the way all the time. This is why when he overdoses on the tea that lowers his anxiety (and the flashes we get of him after he gets his anxiety under control), he seems like a different person.
Lucius- Doesn't like looking people in the eyes. He'll look at people, but direct eye contact makes him really uncomfortable. Also takes care of people to the point of being overbearing at times (Blake was once forced to stay in bed for two days because Luce caught him sneezing).
Not too many now that you mention it. One of the characters in the comic has a habit of puffing her cheeks. And the main character has a bit of a twitch in her left eye when she's nervous that's been present since childhood. There might be more but I can't think of them at the moment...
Ehehe ok, some characters from Narwhal's Song:
Sami: she loves to find paranormal explanations for stuff she doesn't understand, and she's very stubborn when people give different opinions on those subjects.
Mindy: she just really likes to be annoying and to confuse people??
Ruma: idk if that counts as a quirk lol, but they're always on phone checking social media or to-do lists, and they also love to micromanage their relatives.
Jeramy: he's the kind of person who quickly adopts the style and habits of people he admires without noticing it, and he doesn't really respect personal space (at first in Narwhal's Song he's a kid so I guess it's normal, but a few years later he'll still have some childish habits...)
Other characters from the same story, but who didn't show up yet:
Myran: likes to pretend he's very relaxed, but gets anxious easily and fidgets with his hair or jewelry. Also likes to talk to plants.
Bastian: he kinda is religious figure, so he really hates doing small "bad" stuff (like forgetting to say thanks) even tho his superiors say it's ok.
Athos: in the same religious position of Bastian, but has a cycle of not caring about behaving badly, then regreting it, then forgetting he that regrets his actions and doing something wrong again the next day. Also very self conscious about his appearence but pretends he doesn't care. Also doesn't talk to anyone before having coffee in the morning. Also can't hold a baby sheep without crying, even if it's just a toy.
Licole: sometimes likes to eat grass (it's a long story...)
Ned, my character, can't talk right
Like he will say Fluor instead of floor
Pocker instead of pocket
kerchurp instead of ketchup
etc
I haven't had much of an opportunity to reveal some quirks in the comic yet, but my time in an RP revealed a few things about mine.
Rip Vykirson
Has a hatred for vegetables, that extends so deeply that he finds vegetarians and vegans to be his mortal enemies.
Also he's obsessed with uncovering a conspiracy involving Dino Fairies.
He's also notorious for botching people's names, very badly.
Man, I haven’t ever really thought of character quirks before. I don’t think any of my characters do. Wait...maybe?
Bovizo: This is the only guy I can think of. He has a buff complexity, where he has to be bigger and stronger than anyone in the room. He also takes great care of his wavy orange hair. He usually doesn’t wear a shirt. Not sure if those count as quirks, though.
Yeah, they count as character quirks in my book!
Also my character Akros doesn't wear shirts either so maybe they can become best no-shirt buddies 
I've written about a lot of people with varying degrees of damage, so I'll just hit the highlights without spoiling too much.
Gertrude "Tommy" Tomkins was born to high society, yet didn't fit in there due to an extremely severe stutter. She worked around her speech impediment by singing or by speaking French, which gave her no difficulty.
Jacqueline Cochran was rather deeply ashamed of her "poor white trash" roots. I think this helped give rise to her very hard-driving personality and a competitive streak so fierce, she didn't get along easily with WASP co-director Nancy Harkness Love. Even after Jackie's fame and fortune were well established, she still claimed her parents had adopted her.
Mildred Hemmons Carter always wore a flight suit even when on desk duty, as if to assert that she was every bit as qualified a pilot as the men she served with and was only kept mostly on the ground because of stupid reasons. Because it was the 1940's and she was a Black woman, it was all the more remarkable that nobody had a problem with that small show of defiance.
Only two of the main characters of Splitting Image have actual quirks of note which aren't defining parts of their character, so here it goes.
Mortimer - Likes to ramble for no particular reason, sometimes surprising himself with the amount of extras he can add to a simple answer. Tugs and grabs at his arms/shoulders when stressed, even before other things came up on his life. Dresses in whatever looks good even if it's not "traditionally masculine", including having elegant hair styles and actual dresses. Loves to watch birds in the woods when he's feeling good, and loves herons around the lake especially.
Veriesin - Eats messily, unless the importance/politeness of cutlery is immediately necessary. Trains late at night, sometimes consisting of running on the mostly empty nighttime town making as little noise as possible. Doesn't get any specific urges when she changes into animal forms but if she stays in mammals for too long she gets itches from all the fur shapeshifting.
