Down with Love - Renee Zellweger's character stops being a wimpy woman and dyes her hair red to show it.
Charlene, played by Amy Adams in The Fighter, who delivers the immortal line "Don't call me a skank. I'll rip that nasty hair right outta your fuckin' head."
Rose in Titanic (1997) is a pistol even when she's being polite. At lunch she tells Mr. Ismay that Dr. Freud's ideas about the male preoccupation with size might be of particular interest to him. When Cal tries to stop her from going to Jack she tells him that she's rather be Jack's whore than Cal's wife and spits in Cal's face.
Diamonds Are Forever. When James Bond first meets Tiffany Case, she's outspoken, quite rude to him, and has a bit of a temper. She changed wigs (from blonde to brunette), then appeared as a redhead.
James Bond: I don't care much for redheads. Terrible tempers. But somehow it seems to suit you. Tiffany: It's my own.
The Ur-Fiery redhead, Mary-Kate Dannaher in John Ford's The Quiet Man. As another character puts it, "That red hair is no lie!" She tries to slug out John Wayne himself! Maureen O'Hara's finest Fiery Redhead hour.note Maureen O'Hara was a real-life example herself: during filming of one scene where John Ford kept complaining about her reacting to her hair being blown into her eyes, she snapped "What would a bald son-of-a-bitch know about getting hair in his eyes?!"
Almost any character played by Maureen O'Hara. As one of early Hollywood's most beautiful redheads, and an actress willing to play Action Girl roles as much as hot-tempered love interests.
Ginny Weasley from Harry Potter is a double subversion as she is usually soft spoken but:
Harry: Okay, so this morning I'm going to be putting you all though a few drills, just to set things straight... [Everybody keeps talking] Harry: Quiet, please! [Nobody listens to him] Ginny: SHUT IT! [Silence] Harry: ...thanks.
In fact, many of the Weasleys fit this trope. Ron is probably the most obvious example, being a man of short temper and many soft spots, like his family's financial straits, his inferiority complexes (in plural), his romantic inaptitude, mudblood shaming, and pretty much anything that comes out of Draco Malfoy's mouth.
Sean Cassidy/Banshee from X-Men: First Class. His actor even auditioned because it was a rare ginger superhero. Ironically, Sean's one of the least hot-headed and combative of the students, with those titles going moreso to Alex and Raven.
Joseph: I warn you. That redhead has a bite that stings.
It (2017) has Beverly Marsh, a tomboyish redhead, while a very nice girl, is not afraid to get into a physical altercation when someone tries to hurt her or one of her friends.
Henriette de Nevers is an understated but still adventurous redhead in the film version of La Reine Margot.
Gimli of The Lord of the Rings has red hair with a matching beard as well as being quick-tempered. Well, the temper part is kinda obvious because he is a Dwarf. Same goes for his father Glóin in The Hobbit.
Spirited Ashley in Junebug is a midler and realistic version of this.
Lil from the appropriately titled Red-Headed Woman, who is a gold-digging seductress. If you break a date with her, she may follow you to your house and scream at you while you are talking with your wife. If your party upstages hers, she may show up and make a scene. And if you dump her, she might pull out a gun and shoot you.
Murph in Interstellar, who is as brilliant as she is mercurial. More literally when she sets Tom's crops on fire to cause a distraction and sneak back to his house.
Sarah Harding in The Lost World: Jurassic Park. She is an animal enthusiast that studies predators and when she has the very chance of meeting dinosaurs she doesn't doubt for a second, despite Ian's rantings and warnings.
Cynthia in Love Finds Andy Hardy. Cynthia is gorgeous, and apparently quite a bit sluttier than all the other girls in Carvel—Andy doesn't know how to deal with Cynthia's nonstop desire for "hugging and kissing." Cynthia dumps Andy like yesterday's garbage after she gets a look at The Alleged Car he just bought.
The Pontipee brothers from Seven Brides for Seven Brothers are all short-tempered redheads who'll break into fights at the slightest provocation. Frank is easily the best example as he starts fights whenever one of his brothers uses his Embarrassing First Name. The producers deliberately made the brothers redheads to better contrast them with the darker-haired townspeople.
In Life With Father, the new maid watches with trepidation as the Day family's four sons each come downstairs to breakfast, each of them as redheaded as the last (they are not so much fiery, but their father certainly is; his very loud imaginary argument with the mayor frightens Annie into quitting on her first day).
Stealing Heaven: Héloïse, who has flaming hair and a bold, inquisitive personality. Both her beauty and intellect clearly charm Abelard, along with other people.
Rose-Lynn in Wild Rose (2018) has bright red hair, and is temperamental and immature. Visually, it helps her pop against the dreary gray and brown of Glasgow.
Red Sonja: Sonja is a red-haired, hot-blooded swordswoman who has righteous fury for Queen Gedren, who had her raped and ordered Sonja's family slaughtered, on whom she has sworn vengeance.