Faye in Questionable Content. She's also a bit of a subversion, as she's aware she has "issues" and is currently seeking professional help for them. (Even if she agreed to seek that help in order to avoid the other elephant in the room (Marten's feelings towards her)) The Tsundere attitude itself is lampshaded and deconstructed when Raven points out that these things may have consequences. Also lampshaded by a shirt with the word 'Tsundere' printed on the front which she occasionally wears. Interestingly, the shirt was a gift from Hanners, who wasn't entirely sure that Faye would understand the reference.
Dora herself, particularly as shown here when finding out that Marten had a girl flirt with him.
Hell, the Harsh type is essentially the selling point of Coffee of Doom the coffee shop Dora owns, as its customers seem to enjoy being served by the tsuntsun Faye.
Kate in Misfile alternates between this and Kuudere. She's not in love with the protagonist and treats him/her as a little sister. But Ash is still one of the three people in the comic who can draw out anything resembling deredere from Kate. We could assume she's softened up for Harry a little, since she acts as his secretary without complaint and eventually marries him. For the most part her face is blank now that her sister isn't haunting her, but the temper Kate had? All natural.
Aubrey started out as this in Something Positive, but she's gotten to the point where she uses words before her fists. She still has a sharp tongue though.
Torg: Sasha's over here just about every day, curious why you're ignoring her. What am I supposed to tell her?
Riff: Whatever you want.
Torg: This is more than just a little creepy, Riff.
Riff: "Creepy?" Torg, it's about Gwynn!How do I explain to my current girlfriend that my ex-girlfriend, currently demon-possessed, is haunting my dreams and might be stopping by any day to collect all our souls?
Torg: No, that's not creepy. I was talking about Sasha. She isn't hurt or angry, just curious.
Hayasaka Erika from Megatokyo. She's bitter and sarcastic most of the time, and has occasional violent outbursts. When she first met Largo, she broke his arm. But when Largo shows he respects her for who she is, not the star she once was, the deredere comes out in full force.
Also Miho and Piro.
Miho generally hides it under scorn, but once you get past that she's stereotypically Harsh.
Piro is a bit of a weird one. He's nice to strangers, frustrated with Largo, and Sweet with his girlfriend (though he's pretty good at keeping the tsuntsun from getting out of hand). When he's talking about/to Miho, however, he goes full Harsh.
Lynda of Penny and Aggie, towards Rob, in the "Modern Maturity" arc which flashes back to their high school years. Justified in that Rob shows his affection by teasing and pranking her, provoking angry and even violent reactions. She begins to warm up to him when he reveals he has a caring and thoughtful side.
Lucy from Bittersweet Candy Bowl is a pretty excellent example of this until she finally admits to her feelings for Mike.
Actually, Lucy is a Deconstruction of the Tsundere trope. Her punching and striking Mike is not played for laughs, and Mike's reaction to this and the consequences of her behavior is arguably a realistic depiction of what a real, hard-core Tsundere would be like.
BLU Scout from the Team Fortress 2 webcomic Cuanta Vida. His relationship with Bleu mostly consists of following him around, hurling gay slurs at him, and occasionally complimenting him under his breath... until he confesses that he thinks he's gay, and attracted to him.
Vriska abuses Tavros, but claims her true motivations are to make him stronger in the end. Whether she's lying or not, it's implied this is a form of flirtation. It fails miserably—poor Tavros is so frightened of her tsuntsun side that the deredere side never even occurred to him. She later treats John in a more straightforwardly Tsundere way, her occasional moments of touching kindness throwing her typical cruelty into sharper relief. She also tones down the cruelty a lot, partly because she's not in the same location as John and therefore can't, say, toss him off a cliff and break his spine.
Karkat behaves this way. His default attitude is to rant and yell at basically everyone he comes across, but he has very occasional moments of adorable* sorry, adorabloodthirstydere. In his relationship with Terezi, in particular, this trope is played with, in that the tsun is also implied to be romantic in nature. Here, he accuses himself of being a tsundere to Terezi in order to pursue both a hate-basedand a love-based romance with her, and thus keep her all to himself.
He even does a classic tsundere move here, apologizing to Jade and calling her "idiot" in the same breath.
Susan, in El Goonish Shive, is a mild example. Her outward attitude towards most strangers is cool, aloof, and snarky. Then, when she reveals her inner Susan, she can be playful and fun. The latter is rare, however.
Natani, from Twokinds. She has a crush on Keith, but love isn't one of the defining qualities of a hit-and-run assassin. Having a supposedly male personality doesn't help.
Yuudai from Sakana is very tsun around his co-workers, and very derearound his cat. The moments where he actually shows his kind side to them are rare indeed. He is not a bad guy, though.
He is also notably flustered when Taisei is not put off by Yuudais Jerkass behaviour and instead immediately accepts Yuudai as his friend and pulls him into some sort of "bro hug", thus invading Yuudais normally well-protected comfort zone. He then begins to treat Taisei a bit better and even defends him when someone yells at him and treats him rudely, showing that he does care.
Peridot the Witch from Cucumber Quest is haughty, grouchy, and downright dangerous if she decides to fling a petrification spell your way. And yet, she goes strangely flustered and pink in the face when the Legendary Hero's swashbuckling little sister is around...
"I'm not taking this (gift) because I need your pity or anything, okay??"
Anak Zahard of Tower of God had a mother who was constantly bemoaning her marriage, insulting her husband and arguing with him over everything, but it's pretty obvious the women was madly in love with her husband and as Anak states, the only misfortune her mother ever faced in her life was his death.
Yamaguchi-san of Krakow is an Ax-Crazy parody of the trope. She only reveals her "dere-dere" side while drunk. She claims that all Japanese women are like this towards the ones they like, which is one reason Japan has such a war-torn history. Cue a scene from the Warring States Era featuring a female ninja attacking Oda Nobunaga while calling him a "baka".
Sarah Williams' portrayal in the Buildingverse... "no matter how she likes to deny it" to quote the artist of Girls Next Door. This was even lampshaded by Jareth's dark side in Roommates, after he confessed his love and just before he did what probably many characters unlucky enough to be blessed with a tsundere dream of. Tried to murder her.
Feferi Peixes is usually a Genki Girl, and- as Sollux puts it- "sickeningly sweet". Yet she responds to insults with swift, furious remarks. Within a few sentences she's always back to sweetness, as exemplified in her breakup with Eridan and feelings jam with Sollux.
Sollux:(in response to Feferi inviting Kanaya into the horn pile) Of course there's no room. It was kind of a moronic invitation, to be honest.
Feferi: Hey, shut your mopey blowhole! I was just showing a little courtesy. Really, you are just the grouchiest dude sometimes. And it's really cute.
Parodied somewhat with Chiaki in Sparkling Generation Valkyrie Yuuki where the character in question is left in utter bewilderment by her own jumps between happy and exceedingly depressed explaiming that she has "No idea how she should feel!" Truthfully, she's more of a genki girl, but...
Parley from Gunnerkrigg Court won't stop pestering her medium class colleague Smitty with arm locks and noogies and anything that requires her to put her arms around him. He puts up with her treatment because he thinks she's "hotter than hell". After she did finally admit the obvious, we find out that Smitty "don't mind too much" annoying things that happen because of her either... in part, because of her attitude.
In General Protection Fault, a grown up Sydney in the Bad Future acts like this toward Todd, expressing irritation at having to save him from police bots and his defeatist attitude regarding the rebellion, but sees him off on his time traveling mission with a kiss. According to an older Professor Wisebottom, she has loved him for years but has never told him.
Yuki from Ménage à 3 is extremely Sweet towards Zii, and extremely Harsh to Gary. In fact, she's leaning towards being a deconstruction, since her tsundere tendencies lean uncomfortably towards yandere, and she's starting to realize how destructive that behavior is.