The Love TriangleJean Grey / Cyclops / Wolverine from X-Men has long been a complicated storm of controversy. Many fans have shipped Wolverine /Jean Grey since the day Wolverine joined the X-Men, but Marvel has long refused to give into fan demands. So fans engage in Scott and Jean bashing. Marvel has also changed Cyclops (first having him abandon his wife Madelyne Pryor and newborn son Nathan Summers, something not even Jean approved of and later dealing with his post-traumatic astral possession stress by psychically sleeping with reformed villainess Emma Frost (who was also changed into a Tsundere Sue), who agreed to the sort of kinky sex/role-playing Jean refused to engage in — while they portrayed Jean Grey as a forgiving and enabling saint who ultimately gave her blessing to Scott and Emma on her deathbed). Meanwhile, perhaps spurred by those who dislike the often misogynistic views upon marriage that Marvel takes (that is, it's always the woman's fault if a marriage fails in a Marvel Comic), Marvel in recent years have portrayed Wolverine as refusing to consider a relationship with Jean out of respect for Scott, even going as far as to reject a desperate Jean's advances when she confided to Wolverine that Scott was refusing to touch her sexually. So, the Bad Ass is "always right," and his love rival is "always wrong". <sigh>
Their rejoicing was hilariously cut short when Cyclops turned out to be Not Quite Dead, staged a return, and angrily optic-blasted Wolverine off the team. And when Jean found out about Wolverine's Murder the Hypotenuse plan, she threatened Wolverine with all sorts of Mind Rape if she ever caught him having even one romantic or sexual thought towards her.
Then there were the Pete vs. Piotr Flame Wars. When Warren Ellis first hooked up Pete Wisdom and Kitty Pryde in Excalibur, Colossus' initial reaction was to beat the dogsnot out of Wisdom. This, even though in his most recent previous appearance Colossus had come across as level-headed and wasn't even thinking of Kitty. Ellis himself admitted later that he wrote Colossus Out of Character. Alas, the damage was done; Colossus is still reviled by a vocal sub-group of X-fans for one Out-of-Character Moment. Many Pryde/Wisdom fanfics treat Colossus as mentally retarded at best and a rapist at worst.
Following the films, Iceman gets this now from rabid Romy fans. In the comics, Bobby and Rogue were just close friends, but recieved a Relationship Upgrade in the films (Which is then adapted into the Ultimate universe), and with the third film and Bobby being tempted to cheat on Rogue with Kitty (Again, happens in the Ultimate universe too), people now, whenever writing stories based in those universes, will write him off as a despicable, cheating bastard or just out right say they hate his guts now based solely on the Film Script writers.
Any female that "gets in the way of" Batman familyHo Yay is almost guaranteed a vilifying in fandom. Catwoman is exempted because of the Grandfather Clause and her already being a villain; no one else is safe. Similarly, Lois Lane is often conveniently ignored as if she didn't exist when there's Batman/Superman Ho Yay to be had.
The general exception to this rule is Stephanie Brown (aka Robin IV), formerly Tim Drake's (Robin III) canonical love interest. While most of Tim's love interests gets deliberately ignored by Ho Yay shippers, they generally love Steph and her history with Tim. Except in the cases of Kon/Tim fans who hated her, although it was mostly limited to a Vocal Minority.
There have been many fights about who Dick Grayson should be with; Tamarean Princess Koriand'r/Kory/Starfire or 'Batgirl/Oracle' Barbara Gordon. Even the writers got into that one: see the Teen Titans example for details on it.
It's been said that you just don't get between Wonder Woman shippers and Catwoman shippers when they're fighting over Batman. Sorry, but you just don't, if you value life and limb.
One baffling example of the trope happened not to a love interest, but an infant: When the Catwoman title had Selina give birth to her daughter Helena, the revelation that the child was not sired by Bruce caused some angry fans to begin calling for Helena's death as they felt she was in the way of Batman and Catwoman ever truly being together, as well as feeling that Sam Bradley being the father was an Ass Pull. Although Helena wasn't killed off, she did get conveniently written out as being given up for adoption. Come the New 52 reboot, any existence of Helena Kyle has been retconned out (although a rebooted Helena Wayne as Huntress does exist).
In the Watchmen fandom, Rorshach/Dan shippers tend to turn Dan's canonLove Interest, Laurie, into either a) a shrieking harpy who either b) dies horribly or c) turns into a supervillian. Or all three. This allows Dan to be with his true love, Rorshach...who is a homophobic, right-wing ugly nutjob who never bathes and has No Social Skills. Oh, fandom.
There are actually a fair number of Wonder Woman/Superman shippers (not nearly enough to outnumber the Clark/Lois fans, but they exist) who excitedly fantasize about the possibility of Clark and Diana getting married and giving rise to a dynasty of Kryptonian/Amazonian super-babies. Bonus points if their first super-baby is a daughter who can grow up to inherit the mantle of Queen of Themyscira AND the mantle of Last Daughter of Krypton (Supergirl is either conveniently ignored, or goes into retirement so that Clark and Diana's daughter can become the new Supergirl). These fans unsurprisingly villify Lois Lane as an evil, shrill gold-digging "mere mortal" who is holding Clark back from realizing that his true love is Diana, and conjecture that Clark is only truly happy when he gets out of the house and goes on missions with Diana.
While few shippers kill them in fic, shipping Diana with Clark or Bruce is still a huge Broken Base issue and a great way to start a flame war at any comics forum. Rama and Io, on the other hand, Diana's two most obscure suitors (one was in a storyarc nobody read, and the other is a female love interest too subtle for most fans to pick up on), are generally liked by anyone who's heard of them and are probably protected from this mostly because most fans aren't aware of them.
This is actuallycanon for Lois Lane in many Elseworlds, where the writers are constantly offing her so that Superman can hook up with Wonder Woman. One example is KingdomCome, in which Joker kills Lois. This has been so jaw-droppingly overused and cliche, and the Supes/Wondy romances have traditionally been so appallingly badly developed (Sturgeon's Law dictates that most Elseworlds be pretentious original stories with superheroes' names shoehorned into the plot), that it has given rise to all sorts of massive Unfortunate Implications, from the general feeling that Diana spends her life stalking Supes while waiting for Lois to kick the bucket, to the Family-Unfriendly Aesop that superheroes are vastly superior to us Puny Humans, and should not defile themselves by marrying one of our mortal female lumps of flesh.
Happened IN-CANON to Lana in "Whatever Happened to the Man of Tomorrow", the official ending of Silver-Age Superman. Lana was fried by Lightning Lord so that Lois and de-powered Clark could live their life together in the end.
Reversed recently as now it's "Live for our Ship," with many fans arguing for Gwen's resurrection given how much of a "match" she is for Peter over the more popular Mary Jane. Unfortunately, many of these fans fail to ever state a single instance before Gwen died of her compatibility with Peter, and mostly use examples from the recent cartoons and movies featuring her character as "proof."
It should also be noted that while Gerry Conway did prefer Peter and MJ, the decision to kill Gwen didn't come from him. He initially wanted to kill Aunt May, but was told it'd give Peter Parker no reason to keep his secret ID. So Gwen was chosen by the writers and editorial as a suitable second choice. It was hardly the "Writer kills beloved love interest to shack up his fan preferred pairing" some claim it to be.
Green Arrow is often vilified by Dinah/Babs shippers because of his and Dinah's relationship. They even bashed him when he was dead, but nowhere near as much as they've done since he was resurrected. It's just gotten worse since he and Dinah tied the knot, with Ollie's writers apparently liking to help the shippers with that. This may be why the other male in the picture, Dick Grayson of Robin fame, gets almost no abuse.
Now that Green Arrow ended up with Chloe Sullivan in Smallville, some fans are hoping that Ollie and Chloe will get together in the comics now that Chloe's been officially introduced into the DC Canon. The Ollie/Dinah shippers will then shriek that the Ollie/Chloe shippers are "not true comic fans" because they watched Smallville and that this apparently means that the Ollie/Chloe shippers are somehow not allowed to have any opinions on comic characters.
Believe it or not, The Joker gets this a lot from the Ivy/Harley shippers. Justified in that Ivy does treat Harley better... somewhat.
Conversely, if you ship Harley with anyone else, be prepared to duck. There are some fringe extremist Harley/Joker fangirls will attack you and whatever character you ship her with - violently. This would probably embarrass most Harley/Joker shippers.
Harley gets a lot of this from people who want to see the Joker with Batman or (among people who mostly watch the movies) Scarecrow. This is goofy because Harley and Joker have broken up in the comics and are now both free to be shipped with anyone.
And now the Harley x Scarecrow shippers have started in on the Joker, as evidenced in multiplefan videos for the pair on youtube. Actually, probably all the alternate Harley pairing shippers have started in on him.
The comic version of Teen Titans has as much of this trope as the animated version. One case? Beast Boy and Raven. When Geoff Johns made the two an Official Couple, there was mass rage from not only Beast Boy or Raven fans that didn't want them paired up, but also Beast Boy/Terra fans, Beast Boy/Terra II fans, Jericho/Raven fans, Beast Boy/Cyborg fans, Nightwing/Raven fans... fans of any pairing other than the two together. Much hate was directed at Beast Boy from the fans who were more sympathetic to Raven and invoking this trope for him, while fans more sympathetic to Beast Boy began calling Raven an evil slut and scrambled to show their canon proof that she would be an abusive and cruel girlfriend to him, as well as stating that he would surely become weak and turn evil because of her. For some of those on Raven's side, kissing the 'green puke' ruined her forever. Of course, it didn't help that the pairing also lacked stability and much on-panel development through the volume 3 run and Winick's "Titans", with Johns first breaking the two up so he could put Beast Boy on the Doom Patrol (feeling that the Titans needed less adults), and then later writers going back and forth on whether the two would get together or not. They finally settled on continuing their relationship at the end of volume 3, but then the reboot hit.
However, the Beast Boy/Raven fans were not entirely innocent themselves. Some of them had bashed and wished death on any other woman that other fans dare suggest get paired with him, like the later two Terras or Flamebird. They got one wish when Terra II was killed off. Terra III (Atlee) was then erased by the New 52 reboot, and Bette Kane now has no connections to Gar in the new continuity while the first Terra has been rebooted as a hero. The New 52 reboot thus resets the ship war to being between the first Terra and Raven. To complicate things, in the finale of The Ravagers, most of the Ravagers (including Terra) have been captured. Beast Boy was left for dead, but Raven finds him and takes him to the Teen Titans to combat Trigon.
Cassie Sandsmark was hated by some shippers for her relationship with Kon-El, partially for her personality becoming increasingly obnoxious (though depending on who was writing her), and also because she was considered "in the way" of people shipping Robin and Superboy together. Even further back to the Young Justice days, Cassie earned controversy due to Peter David killing off Kon's previous love interest (Tana Moon) in favor of her, making a canon example of this trope unrelated to slash.
During Bryan Q Miller's short run on the Titans, he attempted to have Aquagirl actually get in the way of Blue Beetle and Traci 13's relationship. The result? Enraged fans called for the character's death, referring to her as "The Aquaslut". Although in the end, Blue Beetle and Aquagirl didn't get together.
A few old-school fans still wishing that Kid Flash/Raven would have happened can be rather vitriolic towards any of their later love interests, such as Linda Park (who Wally married). Although, some have also been accepting of Linda and don't approve of DC having erased her (and thus Wally, their marriage, and family) with the reboot.
When it comes to The Flash, as detailed above, Wally West fans that don't accept Linda as his wife have preferred she'd get out of the way for their own favorite love interest. This can include such options as Raven, Magenta, or Donna Troy (who he had an unrequited crush for).