Adaptation Displacement: Partly due to No Export for You not many people realize that this series was based on a still ongoing Light Novel series (starting February 2015, the official English translation of the first three light novels were released in US).
Was Shinra's father a scientist who was curious about Celty and vivisected her to better comprehend her physiology or a psycho who likes dissecting unusual things and getting his son to participate, leading to a strange Yandere obsession with her?
Some fans dislike Ordinary High-School Student Mikado due to his bland personality, being Overshadowed by Awesome, and by extension the Dollars, calling them annoyingly preachy Designated Heroes. This is mainly because Mikado shows hints of a Holier Than Thou personality and also maintains hypocrisy concerning the Dollars, as he states he founded them to show people that "the world still has some good left in it" but used them mainly to fight his own personal battles. This is more noticeable when compared to Masaomi and Anri's motivations, as both of Mikado's closest friends never say that their actions are meant to be heroic or morally right.note This is only in the anime, as the light novels leave out this explanation. LN!Mikado founded the Dollars in an attempt to make his boring life interesting, making his motivation closer to For the Lulz than anything. Not that it stops the fans from putting him as a uke to almost every male character in the series.
Is Aoba a Jerkass Woobie, or is he just as much of a sociopath as his brother?
Some viewers hate him because of his manipulation of Mikado, his Smug Snake exterior, and for having a pretty weak Freudian Excuse. However, others think he's adorable, in spite or perhaps because of his jerkass tendencies. This is mostly due to the anime making him seem more petty.
Speaking of cargo ships and Shizuo, Saika really has a thing for Shizuo. Anytime Anri so much as looks at him, the Empathic Weapon gets terribly excited and begins incessantly whispering, "I love you," in her head.
There's a general consensus that Mikado'sballpoint pen tops Aoba... it's not exactly a loving relationship though.
Saburo with his van according to some, and given how protective he is of it there may be an element of truth to this.
There have also been some...interesting fanworks involving Izaya and his switchblade.
Celty and her motorcycle. Her motorcycle is also a headless horse. This does not make things any better.
In fact, in pretty much all the anime's season finales Izaya gets some sort of violent retribution; he's stabbed in Shou, thrown against metal in Ten, and beaten bloody by Shizuo throughout the last six or so episodes of Ketsu.
Crosses the Line Twice: Seems to be a common theme in Narita's method of characterization; name one main character, and he'll have come up with a quirk or scenario that can topple you out your seat in several ways.
Designated Hero: Quite a few fans' reaction to the Dollars, especially their leader Mikado. The fact that the anime adds quite a few more scenes detailing their heroic motivations despite not showing them doing very heroic things only adds to the reaction (the Light Novel is more morally ambiguous). The main line of reasoning for the anti-Mikado camp is that no matter how noble the overall goal is, using strangers from the internet, sometimes putting them in danger, to serve his own ends is hardly heroic. As for the members themselves, they're at best easily-misled sheep and at worst just as unfitting of the heroic label as their leader.
Later in the novels, they lose this title, mainly because they've stopped trying to be heroes at all.
Ensemble Dark Horse: When it comes to a trio that everyone loves to place together to look or be cool, whether it be in videos or fanart, 9 out of 10 times— it'll be Izaya, Shizuo and Kida. It's also likely that most would replace Kida in that lineup with Celty, as that specific trio ended up as the show's main representatives in majorcrossover appearances.
Oh yes, this definitely applies to Izaya. He might be an unapologetic Troll who enjoys ruining people's lives For the Lulz, but he's just so smooth, charming, and brilliant that most fans Love to Hate him, if they don't just love him outright.
If you look on Fanfiction.Net, Deviant Art or any other poll site, you'll probably notice that Shizuo/Izaya is the most popular. Doesn't help with the Ship Tease that Narita gives to bait the fangirls.
The most popular ship with Mikado seems to be Izaya/Mikado. Either because of how Izaya gets paired with mostly everyone, because of the subtext they have in the novels, or both. In japanese DRRR fandom, it might actually be the second popular ship with Izaya after Shizaya.
Shizuo/Izaya (which is regularly spoofed, lampshaded, teased, and generally dicked around with), Shizuo/Vorona, Mikado/Aoba (which overlaps with Ho Yay, and Namie/Mika. Erika claims to see some between Kadota and Chikage.
Izaya Orihara is an information broker and one of the most dangerous men in Ikebukuro wanting to declare his "love" for humans by manipulating them for his own amusement. Introducing Masaomi Kida to his follower Saki Mikajima she would have Saki form a romantic relationship with Masaomi while Izaya instigates a gang war between Masaomis gang, The Yellow Scarves, and The Blue Square, leaving Masaomi vulnerable, endangering Saki, and dismantling both gangs in the process. Also a member of The Dollars, Izaya has recruited thousands into the Dollars before turning them against their leader by reveal to them his identity, Mikado Ryuugamine, allowing them to reek havoc throughout Ikebukuro. After being stabbed by "Jinnai Yodogiri", Izaya would allow himself to be capture, tricking his captors into revealing information on "Jinnai Yodogiri" before sending his newly formed group to defeat them afterwards. Also holding immense animosity for Shizuo Heiwajima for not being able to manipulate him, Izaya has provoke Shizuo constantly, cost him his job, frames him for murder, manipulates a girl to kill Shizuo, and tries to kill Shizuo himself. When Shizuo manages to beat Izaya, he attempt to goad Shizuo to kill him, content that the masses witnessing Shizuo will then view him as a monster.
Kasane Kujiragi is a Dhampyr who uses the name "Jinnai Yodogiri" to orchestrate the events of 2x. After Izaya Orihara ignores her warning to not interfere with her plans she has him stabbed and later interrogated for information, before allowing him to continue manipulating people to keep them distracted from her own scheming. Also a wielder of Saika, Kasane would hand over Saika to Shingen Kishitani having him spread Saika throughout Ikebukuro creating more Saika wielders and expand Saika influence to almost everyone in Ikebukuro giving Kasane complete control over masses minds and the city. She would also posses Shingens son Shinra to make Shinras Love Interest Celty Sturluson more vulnerable allowing Kasane to defeat her and give Celty her head to put her under Kasanes control. Kasane would later save her half-niece, Ruri Hijiribe, from her stalker while taking full blame for the crimes Ruri committed as the Hollywood Serial Killer, so that Ruri can continue living a normal life.
Memetic Badass: Shizuo, Izaya (memetic ubertroll) and Mikado (usually in reference to the pen stabbing incident from Volume 6).
Almost every time someone is talking about Izaya, sooner or later "stomping on cellphones" will show up somewhere in the discussion.
Just like the Izaya example, Shizuo is always depicted throwing around vending machines all the time whenever he gets mad even though he actually throws anything heavy instead, or uses the closest street sign as a club.
YO YO YO... HEY MAN!
Mikado is becoming this. Especially his pen.
The first ED, Trust Me, has become an art and video meme; people replace the distinctive character chain with characters from other shows or media.
Mind Game Ship: Izaya has a canon one going on with all of humanity. His favorite targets, however, seem to be Shizuo and Masaomi, as well as the girls he forms "suicide groups" with For the Evulz.
Though with Shizuo it's mostly in the anime; in the novels, Izaya truly hates him and states that he would rather be as far away from him as possible. He also hates talking about him in general and seems to get pissed whenever anyone mentions him. Shizuo's the last person Izaya would try to play mindgames with face-to-face - he just tries to get him dead from afar.
Mis-blamed: Saki. The main accusation thrown at her by fans is that she's responsible for Masaomi dropping out of school and leaving Ikebukuro. In reality, it has very little to do with her. Masaomi left Ikebukuro because he was too ashamed to face Mikado and Anri after the whole Yellow Scarves incident. The extent of Saki's involvement is giving him a place to stay after he ran away from home.
While this is true for the original novel, the anime's epilogue makes it seem that Masaomi left to elope with Saki, and the scene with Mikado and Anri, smiling and being oddly understanding of his choice to leave. This also wasn't helped by the anime giving Masaomi an more angst on the subject of Saki, and basically making Masaomi bring her up when Mikado and Anri saved him, and ultimately having Masaomi beat up Horada in order to take revenge for what happened with Saki. This is a big change from the original novels, where Masaomi beat up the Yellow Scarves in self defense, and after Anri and Mikado arrive the three just sat in silence being happy that they were all right. Anri and Mikado also aren't understanding of why Masaomi left, because he never brought up Saki with them at all, in fact Saki was never the main focus of Masaomi's characterization in those chapters. So this case Saki is only Misblamed, if you're talking about the novel, if you're talking about the anime however Saki's character factors into Masaomi's character more, though ultimately it is still his choice in the end.
Izaya crosses it in the back story with his treatment of Saki and Kida.
Granted, to some, he crossed it upon his introduction. Especially in the novels/manga.
Any amount of sympathy you may have for Haruna will be lost after Anri shows her her depressing backstory. Haruna's response? Ruthlessly and remorselessly attacking her with the obvious intent to kill her, laughing maniacally in the process.
Izumi Ran either crossed this when he kidnapped Saki and broke her legs or when he abused Aoba. It's hard to tell which, though.
Aoba isn't very sympathetic either. If he didn't cross it when he risked burning down his house just to get back at Izumii and subsequently got him beaten by their abusive father, then he definitely crossed it when he manipulated Mikado.
Narm: The manga was brought over the US and published under the name "DRRR!!"... which sounds like a common exclamation indicating that one thinks that something is stupid (i.e. "durr" or "derp"). It's a valid translation of the title... but it's a really poor one.
Never Live It Down: Despite not appearing in the anime until the end of season three, Aoba is best known for getting stabbed with a ballpoint pen by Mikado of all people. This is to the point that, since there are very few official illustrations of him and we don't get a good look at his face, he is usually made recognizable in fanart by his wounded and/or bandaged hand.
One True Threesome: Kururi and Mairu don't seem to mind crushing on the same guys, and they both kissed Aoba. And there's also the Twincest. Of course, this is probably because they don't see themselves as seperate people.
Mikado/Anri/Masaomi actually has a following, due to Anri and Mikado getting a lot of Ship Tease while Mikado/Masaomi gets a lot of Ho Yay.
Saki. Many people think that she destroyed the ¡Three Amigos! dynamic with Mikado, Anri and Masaomi to the point that Masaomi left Ikebukuro with her and fails to communicate with the other two as time goes on.
Seiji, Namie and Mika also qualify; fans consider them insane, even by Narita's standards, and even after their subplot was rendered completely pointlessthey wouldn't stop showing up. Namie gets more Scrappy points to many Shizaya fans for "being in the way of their relationship."
Namie and Mika's scrappy-status is, for the most part, only among anime fans, but this rings especially true for Seiji in the novels. Most people can't understand why so many people like him, because he's very dull and kind of...weird. Mika and Namie aren't as disliked for this by the novel fan, because Namie still has her role as Izaya's secretary, and Mika's been getting more love due to the revelation that there's much more to her than what meets the eye.
Seasonal Rot: It's generally agreed that the first half of Durarara!!×2 is not as good as the first series.
If you don't ship Saki and Masaomi together, she'll always suffer this treatment. (Mostly in the Izaya/Masaomi stories.)
There seems to be some fights between shippers of Shizaya and Izamika/Izakida, mainly due to Shizaya fans complaining about Izaya's manipulative/abusive nature and because of the age difference between Izaya and Mikado/Masaomi.
To a lesser extent, Izaya/Namie and Shizuo/Izaya have also gotten some of this on forums and blogs.
Squick: Episode 12, where we are treated to a scene of Izaya playing around with Celty's head, tossing it back and forth in his hands like it's a basketball. Though this doesn't quite amount to the fact that Seiji is in love with it. And that Shinra loves Celty better without it.
The Twincest between the Orihara siblings can be extreme Fan Disservice to some fans.
Take That, Scrappy!: People who are not fans of Mikado cheered when Chikage gave him a verbal beatdown during season 2.
For the viewers that hated him, Mikado stabbing Aoba in the hand with a pen was pretty satisfying.
Anytime karma comes Namie's way.
Tear Jerker: Admit it, you cried when you thought Shizuo was going to die alone in that alley. Also, Anri's backstory.
And Akane Awakusu's realization that all the people she thought she was friends with were just acting like it because they're terrified of her yakuza parents. You really feel for her when she starts crying over this.
Unintentionally Sympathetic: The anime does this to Izumii. Because his abusive behavior towards Aoba wasn't mentioned in much detail, Aoba setting his room on fire just so he could watch his father beat him makes it seem like Disproportionate Retribution. Since this was before he broke Saki's legs and threatened to rape Earthworm, his worst crime was just being a Big Brother Bully.
Celty is to a few fans- she just wants to get her head back. This, on top of how she possesses some human traits and lives like a normal human, except everyone else has a head! Yeah.
Woolseyism: The English dub of the anime changes most of Masaomi's Gratuitous English uses of the word "erotic" (in reference to Anri) to "boobylicious," particularly in Episode 13. It ends up working better, as "erotic" isn't often used in the same sense in English as he was using it in the original. That, and it's much more in keeping with Masaomi's personality to make up a word on the spot and then keep using it until Mikado tells him to stop. It also just sounds funnier.
The dub makes Izumii more of a Sir Swears-a-Lot. The most notable example was in his A Day in the Limelight episode, where he would call random people "scumbags," but was changed to "assholes" in the dub. For an arrogant delinquent like him, this is arguably more fitting for his character.