In the Two Thousand AD black comedy story D.R. & Quinch Go Girl Crazy, Waldo "Diminished Responsibility" Dobbs has paired up with Chrysoprasia, a drama coach's daughter, and is putting on a respectable front to win her approval. His friend Ernie Quinch is worried that she is falling for his evil, delinquent friend and also breaking up the evil, delinquent partnership of D.R. and Quinch. So he kidnaps her and shows her their home movies, to prove to her that she doesn't want to know D.R. But instead, the horrific experience triggers a mental breakdown leading to a Face-Heel Turn whereby she becomes more evil and delinquent than either of them and reinvents herself as "Crazy Chrissie".
Tim Drake, the 3rd Robin, now Red Robin, started out quite differently from his predecessors. Unlike the first Robin, Dick Grayson, he had a family during his run and a large supporting cast at his school. Overall, he was portrayed more as a realistic teenager than a vigilante. That was until his girlfriend was brutally tortured to death by Black Mask. Later on, his father was killed by another villain, Captain Boomerang. You would think that would be enough, but DC editors would think otherwise. His two best friends, Conner Kent and Bart Allen, Superboy and Impulse/Kid Flash respectively, died saving the world making Tim the last surviving member of the original team they started, Young Justice. They later got better. He has since taken up more of Batman's mannerisms, now being able to put fear into the eyes of his enemies. When you take into consideration that many of these events happened in the time span of a year or so, expect him to be in need of some psychiatric help in the near future.
Before all that, his parents were kidnapped and as they were being rescued. He saw his mother die and his father almost die because of a poison supplied by the kidnapper.
Oddly enough, Cassandra Cain is a mirror image of Bruce. Despite the Training from Hell, she was a true innocent who thought the mastery of combat arts was as much a game as anything and the painful parts (two for flinching, with light caliber handguns) were "normal" to her. Then she reduced a living, thinking, man to a large mass of inert meat with her own 8 year old hand... seeing the horror in his eyes as life faded from them... and it was suddenly not fun anymore.
Jason Todd was broken by dying, even after he was killed off for real, when he became Red Hood.
Batman himself. Watching his parents get shot dead right in front of him... you didn't think a guy in an armored bat costume swinging from the rooftops on a nightly basis to beat up crooks was sane, did you?
Both played straight and for comedy with DCU's Miss Martian, M'gann M'orzz. After One Year Later, it's said she left the Teen Titans due to something Ravager did to her; while fans wonder as to the implications, it's later revealed that Ravager just yelled at her, making her cry, when M'gann threw a pie in her face. Eventually, she is nearly broken when her Future Evil Self's body is destroyed and their minds merge. M'gann eventually wins the mental war by using bunnies and cute images in her mindscape to keep her evil future self at bay.
Do NOT attend the Xavier Institute. Just don't. This goes double if you're on Earth-616. They will kill all your friends, run over your dog, and rip out your soul all in the space of a few hours if you go to the Xavier Institute.
Illyana (Magik) started as Colossus' little sister; after being sucked into Limbo (Belasco's dimension) while at Xavier's, she returned with new magic powers and a severely damaged mental state (to be fair to the team, time differences were so great, she appeared to only be gone a few seconds). She is then returned to Belasco's, where she undergoes a weird process that causes her to split into multiple beings, rather confusing, one being a soulless girl stuck in Belasco's dimension.
Then you get to poor Megan Gwynn, aka Pixie, a girl who (before House of M) was voted most cheerful person at Xavier's. She along with her classmates are dragged into Belasco's dimension, where, in order to escape, team up with the soulless Illyana. In the process, Pixie loses a portion of HER SOUL. She returns with black streaks in her hair (presumably representing the darkness now in her soul) and a magical dagger that allows her to teleport. Then in another arc she returns to that dimension, this time with the main team. Here she attacks Illyana for stealing a portion of her soul and after losing, Illyana takes YET ANOTHER chunk of Pixie's soul and sends the X-Men back home. Later she gets badly beaten by some racists, kidnapped by demons and finds out her parents aren't her real parents and she is really a daughter of Mastermind and some witch. And then she gets to Limbo and has another part of her soul stolen AGAIN, though this time she regains all parts of her soul at the end. And then, along with everybody else, she gets brainwashed by a powerful reality warper into believing her life was one big hell on Earth, which turns her into murderous sex-obsessed psychopath with a demonic look, called Nightmare. And once she gets back to normal, Nightmare survives in her mind as a Superpowered Evil Side. Poor girl cannot catch a break.
Or Longshot - a peppy, happy-go-lucky charmer. WHO HAS HIS SOUL EATEN BY A DEMON in the Inferno storyline. Even when everything goes back to normal, he's left with some serious angst.
If you're a young mutant, this is bound to happen no matter where you live. The only place more dangerous than the Xavier Institute (or whatever the current headquarters of the X-Men happens to be) for young mutants is the world outside of it.
Rahne Sinclair has this in spades. Rescued from being burned at the stake by her abusive father, her life seemed to be getting better once she joined the New Mutants. Cue a long string of traumas — her first love dying to save her, being mind-raped by an evil psychic, her best friend being possessed by a demon, being kidnapped and mind-raped/genetically modified into a mindless slave, seeing another dear friend murdered, struggling to break free of brainwashing, losing her powers and adoptive mother in a single day, and being shown a Bad Future where she murders two dear friends. Then she got recruited onto a black ops X-team, where she would be brainwashed and given a heroin overdose by her father. This resulted in her nearly murdering her teammates, and eventually EATING HER FATHER, a trauma she's blocked out. While being deprogrammed, she was reunited with an old love and became pregnant, only for him to sell his soul to save her. The baby nearly killed her and turned out to be a supernatural beacon for bad things when close to being born. All of this over the course of maybe 7 - 8 years of time.
What was done to X-23 from birth until she escaped, then her handler tracked her down, and what happened wasn't pretty. And what makes it worse is that the Facility was breaking her on purpose. When they decided she had too much empathy for others, they gave her a puppy with orders to kill it. When she played with it instead and failed to carry out the orders they threatened to torture it to death and make Laura watch as punishment. She gets better, and learns to be a normal girl from Jubilee... kinda.
And now, Avengers Arena looks to be attempting to break her all over again...
Little Jean Grey, who begins as the sweetest person at Xavier's. She's the Team Chick and is as cheery and perky as can be. Then, while hunting Proteus, Jean starts having these daydreams where she's slipping into the past, where she is in a rather intimate relationship with a man who is far less straight-laced than Scott. Did I mention that just a little while before this, Jean, dying of radiation, made contact with a cosmic entity called The Phoenix Force who just happened to share its infinite power with her? And that with that power she'd fought Galactus to a standstill and healed a cancerous galaxy? So yeah, Jean keeps having these visions until she can't escape from them. Then the masquerade is over, and Jean realizes she was being used by Mastermind and The White Queen, who have been more or less raping her mind and forcing her to do things that were scandalous to her. Except when the mask comes off, Jean loses her grip on all that infinite power that The Phoenix gave her, and it drives her mad. She's filled with the hunger of a Cosmic being, and the memories of her glorious triumphs. So she breaks down and eats a star. Then the Shi'ar get upset and condemn her to death, and Jean knows there's nothing for it, so she commits suicide to avoid repeating the things she did.
The above did NOT happen to Jean, but to the Phoenix itself, which from time to time wants to know how it is to feel human, and took her memories, looks and personality while the real Jean was healing in a cocoon at the bottom of the ocean. However, after the real Jean has come back and her cloneMadelyne Pryor (read below) dies, Jean is given the memories of both Madelyne and the Phoenix. Given that she also had a traumatic experience at the age of 10, watching her best friend die from a car accident while being mentally linked to her and feeling everything she felt, we can safely say Jean has three sets of screwed up memories in her brain, two of which are of women that looked exactly like her.
Then, when she's revived, the love of her life is with a clone of hers, who has her own breakdown, resulting in a deal with the devil and the return of the Phoenix Force. Then Scott cheats on her with the very woman who caused the Dark Phoenix to come into being. Then Jean dies, and sees a future in which all her friends suffer incredible anguish and, because the Phoenix is as much her tormentor as her friend, it convinces her that the only way to fix all this is making her push her husband into the arms of the woman who caused the Dark Phoenix to come about. Then the Shi'ar slaughtered her entire family. Then they hurt the Phoenix and it forced her back out of the grave, so she had to die AGAIN. Then the Phoenix came back and handed itself into the arms of The White Queen, and with that power, Scott went nuts.
Long story short, the day the Phoenix saved Jean's life, it set her on a very, very painful path.
Can't forget to add in Dust. Separated from her mother (whose fate is unknown), was sold into slavery until Wolverine saved her and becomes enrolled in the Xavier Institute, only for some of her new friends and love interest to die as the comic progresses.
What about Cyclops: his life started going badly when his parents threw him and his little brother out of a plane when he was a young child, leaving him an orphan with brain damage. His life only got worse from there, even more so once he reached adulthood. The level of shit he has gone through since then makes Charles Xavier rescuing him from an abusive criminal seem more like an act of Yank the Dog's Chain than anything else. To put how much Cyke has been broken into perspective, when he first arrived at the school (while still undeniably broken) he was a Dandere. Adult Cyke proceeded into Sugar and Ice Personality to avoid being hurt anymore.
Adrianna Tomaz, aka Isis from 52. She starts as All-Loving Hero, determined to see the good in the world despite all of the horrible things she had endured up to that point (being kidnapped to be used as a bargaining chip by Intergang for starters). As Isis, she brings light to Kahndaq and convinces her new husband Black Adam that he doesn't have to be a violent Anti-Villain anymore. Then it all goes to hell in One Bad Day. Her brother is eaten alive by their Team Pet Sobek, who was really a member of a group of Eldritch Abominations sent by Intergang to destroy the Marvels. Then she gets a mouthful of plague and dies a painful death in Black Adam's arms. Adrianna is so broken that she renounces her idealism, tells Black Adam that he had been right all along about the world, and with her last breath asks him to "avenge us". Believe it or not, it went From Bad to Worse. Being resurrected and brainwashed by an Evil Sorcerer who used her to free himself from a prison and subsequently being constantly raped by said sorcerer sent her soaring over the Despair Event Horizon. When Black Adam eventually frees her, Adrianna's first act is to castrate the sorcerer with her bare hands. Finally, she crosses the Moral Event Horizon into full-blown villainy when she declares the people of Kahndaq, the people who worship her as a goddess, to be just another bunch of bastards, and starts turning them into dirt statues. Even Black Adam is horrified by this!
Stacy Palumbo of Grendel's corruption from a Cheerful Child into a Creepy Child/Broken Bird began from her discovery of her adoptive father Hunter Rose's identity as Villain Protagonist Grendel, the man who killed her uncle. After planning out Hunter's death (and murdering her governess along the way to keep her from interfering) by secretly assisting Argent taking down Grendel's criminal empire and ultimately leading both into their final showdown. After Rose's death she was institutionalized. Just when things are going to look better after a few years with her marrying her therapist, her husband goes ahead and rapes her on their wedding night before hanging himself. Since then she began to slowly waste away in body and mind until she finally dies.
Surprisingly averted in Sin City. The Yellow Bastard was unable to make Nancy Callahan scream... twice. She remained safe and unbroken every time he kidnapped her.
Gwen Stacy: Originally an Alpha Bitch who took a level of Character Development until she became a mature and thoughtful Tsundere Girl Next Door type. Then, her dad died. When she finally managed to get over that, SHE dies.
There's sad history of Klara Prast of the Runaways, who kept talking to plants. Her religious asshole parents convinced her she was the spawn of Satan and married her off, at frickin' age eleven, to a creep who raped her and forced her into dangerous jobs to earn money for him to buy booze. Luckily, the Runaways rescued her and brought her into the future where New York happened to be under invasion by Skrulls. Then they took her to LA where they got attacked by angry rainbow-colored people. And then, just when she was starting to get the hang of our modern world, someone fired a missile at the Runaways' home that came so close to killing her. On top of all that, Marvel cancelled the series.
X-Force did this to Psylocke. Uncanny X-Force started with Betsy Braddock cool, collected, and confident and together with the man she loves. Then the man she loves turns evil. And then she kills him. And then she kills her brother to save reality. And then she's mind-raped after being ambushed by another psychic. And then a second man she's come to have very complicated feelings for sacrifices himself to save her. And then she finds out she causes a totalitarian Bad Future. Post-traumatic stress disorder doesn't even begin to describe it.
Poor KidLoki, you never stood a chance. First he's brought back to Asgard, a place where he's widely hated and mistrusted for things he did which he can't even remember. Sure, at least his brother is on his side, but he's barely ever there. His first companion? Ikol, The spirit of his old, evil self. Then he gets a friend his own age, only she seems to enjoy being as mean as possible to him. And then she leaves. And he gets a dog, too. An evil dog that spits out fire and is obsessed with killing people. And his mother blackmails him into being a spy. And his dreams are mostly nightmares of his past deeds and growing up to be horrible all over again. Then his friend comes back only to betray him and the dog turns on him and what little respect he managed to garner through hard work and doing good is tossed aside when everything comes crushing down on his 13-year-old little head. But, hey, at least Ikol won't turn on him, right?