Abominable. Stephanie mentions the redhead Finn's hot temper right off the bat, right before we get to see his response to Timothy trying to pick a fight with him. He flash steps right up to Timothy, delivers a quick Badass Boast that doubles as a death threat, calls the grown man an insolent child and then tells the guy to get out of his sight.
Redhead Cate Hendrickson of Paradise Rot fits the bill. Sarcastic and Irish as it is possible to be.
In the Branion series by Fiona Patton, the royal family of an alternate Britain is literally this. The sovereigns are the Jesus-style avatars of a fire god, and they commonly have red hair. They also have tempers, which is not surprising given that effectively having a fire god inside you is not good for your mental stability. Justified by the presence in their family tree of Danes, Welsh and Irish.
The Ashtown Burials series, by N.D. Wilson, has the reddish-brown haired Diana Boone. She doesn't have a particularly quick temper, but she is a skilled warrior and ace pilot, and you don't want to be on the wrong side of her when she does get angry.
As is her redhead son, Ben Skywalker. The striking similarities between the two (particularly their personalities) are brought up fairly often in profic, especially in Sacrifice, and a LOT in fanfic. To be honest, probably the only notable physical feature he inherited from Luke are his blue eyes.
Ygritte, a wildling, from A Song of Ice and Fire. All redheads are believed to be "kissed by fire" in the wildling culture and have a reputation for spirit. Averted in Westeros proper, where red hair is associated with the more genteel Tullys. Rickon Stark, however, inherited the Tully red hair and is the most expressive of his siblings, although this may be due to his youth.
Anne of Green Gables. Justified with Anne Shirley, whose temper was at its fieriest when she was teased about her red hair (being one of the few characters whose fire is connected to their coloring). She chewed out the neighborhood busybody and also responded to being called "Carrots" by breaking her slate over a schoolmate's head. Nobody ever teased her about her red hair again, after the social snubbing Gilbert got for five or so years. Ironically, they end up marrying. note It's ironic for Anne. That was Gilbert's goal since the beginning. Anne never quite gets over her dislike of her red hair. She didn't even like it when her children inherited it. When Jem is born and the nurse tells her his hair will be red, Gilbert reports to Marilla that "Anne is furious with her, and I'm tickled to death!"
Princess Eilonwy is the extremely temperamental TsundereAction Girl with long red/gold hair whose temper is feared even by her friends, and especially her love interest.
The boisterous redhead King Smoit, who is jolly and personable with his friends, but unleashes a warrior's temper on those who anger him.
Aviendha (and, to a lesser extent, all redheaded Aiel women) from the Wheel of Time series behave like this. They are quite proficient with the spears and knives they threaten men who make unwanted advances with.
Pippilotta Delicatessa Windowshade Mackrelmint Ephraim's daughter Longstocking, from the Pippi Longstocking series (and subsequent adaptations). Don't mess with this redhead tank of a little girl.
Herrenna the Henna-Haired Harridan, a side character in The Light Fantastic has red hair (per her title) and absolutely no patience or pity for either Rincewind or Twoflower. Oh, and she has a very big sword.
Alanna of Trebond of Song of the Lioness (the first book in the Tortall Universe) has bright red hair and a temper to match. Her squire later remarks how she's known for her sharp edges—sword, knife, and tongue.
Ditto with Tris, a redhead in Tammy's Circle of Magic series. She's very prickly from years of verbal abuse and abandonment. She does eventually warm up to her new friends, but she's still quick to sarcasm and doesn't tolerate fools gladly.
Ce'Nedra from David Eddings's Belgariad. Not just her husband Belgarion, not just their royal court, the entire kingdom of Riva is focused on keeping the flame-tressed Queen Ce'Nedra happy. Because the alternative is just too grisly to contemplate.
Maedhros, Amrod, and Amras from J. R. R. Tolkien's The Silmarillion are the only elves to be described as redheads who fit the personality type. They're fierce, rash, more violent than is really healthy, and not particularly wise or patient... but then so are all their darker-haired siblings. A lot of fans assume their mother Nerdanel's also redheaded, thought the author only ever said her father is, and both of their personalities are the complete opposite: calm, soft-spoke, patient, and wise. They also had the sense not to join the rebellion of the Noldor, which is why they're still alive.
Karen in The Three Worlds Cycle. Specifically in the first quartet, where she appears as a main character. She takes on Rulke, for Io's sake, and harasses every main character through the whole quartet. And she just happens to be described as having "extremely fiery red hair"...
Sarah in Tales of an Mazing Girl has long red hair down to her waist and is pretty firey in the right circumstances, if she often keeps her sass to herself.
Terry Brooks' Voyage of the Jerle Shannara introduces Rue Meridian, a redhead who steals airships single-handedly and kills lizard-men, and you had better not tell her she can't.
The redhead Bronwyn in Bronwyn's Bane. Living with a serious curse increases her anger management issues.
The redheaded Fire-witches in the Enchanted Forest Chronicles deserve special mention: when they get angry enough (which is often), their hair explodes.
Margot Maynard in Elinor M Brent-Dyer's Chalet School series. Her hair is constantly described as 'reddish-gold' and she has an absolutely rotten temper, which she blames on her 'demon'. She tries to control it, but it often gets the better of her, culminating in her nearly killing a girl with a bookend in The Chalet School Triplets. Her cousin Sybil Russell also qualifies, at least as a child, until an accident with a kettle and her younger sister has a drastic effect on her personality.
I, Robot has engineer Mike Donovan, described as possessed of perpetually unkempt red hair, a short temper, and a generally Hot-Blooded personality, in contrast to his calmer dark-haired work partner Gregory Powell.
Princess Elizabeth of The Royal Diaries' Elizabeth I: Red Rose of the House of Tudor is a redhead who can swear up a storm when she wants to.
The main character of the Dear America book A Coal Miner's Bride: The Diary of Anetka Kaminska complains about everything about her looks except her red hair. At one point, she suddenly remembered that she was her mother's fiery redhead and started yelling at her ungrateful husband with a list of the things she does for him.
'Red' Blaze from the Civil War and Floating Outfit novels of J.T. Edson. Blaze is the most hotheaded and impetuous of Edson's heroes.
In Death series: Feeney has ginger hair. He may seem rather calm, but he can be explosive when he's angry.
In the short story "Nobody Here Butó", protagonist Cliff Anderson is deeply in love with his red-haired girlfriend Mary Ann, but does not quite have the courage to ask her to marry him. Throughout the story Cliff talks about how wonderful Mary Ann is, but always amends his statement with "but she does have red hair;" she acts feisty and aggressive because that is how girls with red hair act.
In Asimov's Lucky Starr series, Lucky's sidekick John Bigman Jones has pale red hair, a short temper, and a generally emotional nature. Lucky, on the other hand, is calm and brown-haired.
The princesses of A Brother's Price are all noted for having red hair, referred to as "the royal red" at a few points. Each princess has a different personality and none are exactly mercurial, but strength and passion are part of all of them.
Jessie in High Society by Ben Elton. Her hair colour (dark auburn/reddish-brown) is referred to only once, but combined with her strong personality she is an obvious example of this trope.
Kaylana the redhead druid in Villains by Necessity. Living up to the trope by answering any attempts to approach her with a staff knocked over the poor man's head.
She gives us the redhead Beatrice Löwenström in her debut novel ÷verenskommelser. She's intelligent, competent and assertive. But alas, many people in this era (the 1880s) prefer quiet and subservient women. And being at the mercy of her abusive uncle, who bullies her into a marriage with a man, who treats women like dirt under his shoes, she finds that out the hard way. But she's not afraid to call her oppressors out on what creeps they are, even if that only makes them even angrier with her...
Averted with Beata Jensdotter in "De skandalösa". Despite being a redhead, she's less fiery than the brunette protagonist Magdalena.