Anti-Climax Boss: Being an anime centered in dialogues and not battles, this is expected. The majority of the "fights" of the series either ends quickly or things simply don't heat enough for them to happen, and the antagonists are usually dealt with conversations instead of brute force. The only entry who averts this is Kizumonogatari, who is the most fight-oriented part of the franchise, and here we see in all its glory the fights of Araragi against the three vampire hunters and eventually Kiss-Shot.
Crosses the Line Twice: Koyomi getting into a fight with a 5th-grader, beating her up (mildly), and then laughing about it. The fact that she's already dead may or may not make this worse. The light novel's description of the fight made it worse, detailing liquids that came out of her mouth that may or may have not been stomach acid.
Shinobu at the beginning of the series: Fifth place on the popularity polls while not speaking a single word and getting relatively little screen time is pretty impressive. People who never saw/read the story but at least recognised her almost always thought she was an incredibly important charatcer simply due to the sheer amount of fan-art she got (including a lot dedicated to the bathtub scene). This doesn't applies anymore after Nisemonogatari, since nowadays, Shinobu is a full-fledged heroine instead of a silent supporting character.
Everyone Is Jesus in Purgatory: Fans have theorized that all the oddities simply stand in for otherwise mundane life problems; the ones with the most merit are Hitagi's (her "weightlessness" being caused by an eating disorder—it's noted, for example, that she has become much more attractive in the past few years), Suruga's (well, extreme jealousy, that's barely a stretch there) and Hanekawa's (her problem could disassociative, multiple personality, or bipolar disorder, depending on the interpretation of Black Hanekawa and the Tiger; it might even just be normal lashing out from stress). Nadeko would be "constricted" by the thoughts and actions of the jealous and spiteful, and Mayoi could be the Adult Fear of a child lost forever.
Fashion-Victim Villain: Deishuu Kaiki. A tie you could jump rope with, that one. And that dress shirt is damn near an actual dress.
Fetish Retardant: When the Meddlesome Cat grabs Koyomi from behind, he licks his neck in a very sensual way. What's the problem? That the Cat's tongue is sharp enough to open Koyomi's carotid artery.
Foe Yay: Senjougahara and Kaiki. Kaiki believes that when they first met, Senjougahara fell in love with him (which she denies). The Hitagi End arc revealed that he admired and cared about Senjougahara a lot (he destroyed the cult her mother joined and arranged for the divorce, believing it was best for her). His irritation with her boyfriend and her proposition of prostituting herself implies that it's not a platonic love either. Senjougahara admits herself that she came to enjoy their time together and even flirts with him a little (joking about how he must have been excited to have a high school girl at his command and the color of her underwear). Further fueled by the Koimonogatari OP in which they're like a broken up couple who are still unable to move on.
Harsher in Hindsight: When Tsubasa finds Koyomi beating up Mayoi, she tells him that it's wrong to hit a child without telling them a justifiable reason. We later find out that Tsubasa's stepfather physically abuses her. It's likely a deliberate example; Tsubasa has Scary Shiny Glasses as she makes the former statement.
Bakemonogatari is a slideshow.note The show's frequent use of still frames, especially during dialogue, lead to many people jokingly claiming this.
Kaiki is best girl note Due to Kaiki's awesome role in Koimonogatari, his popularity increased greatly, generating him a great legion of fans, with many of them calling him "his waifu" and "the purest girl of the cast".
The toothbrush scene. Everything about the toothbrush scene. note Nisemonogatari somehow managed to make a person brushing another's teeth very erotic and a metaphor for sex. Often brought up as the height of the Monogatari series's weirdness.
Spooky Ouginote Describing Ougi as such became very popular, particularly around Owarimonogatari's release, due to her bizarre character design and odd mannerisms.
KIZU WHEN?!note Due the constant delays of the Kizumonogatari movie until it was revealed in 2015 that Shaft was planning to do a trilogy, it was common for the fandom to use images or texts related with the never comming release of Kizumonogatari.
_______ Circulationnote There are quite a number of videos on the internet which puts raps or other pieces of music to the instrumental and giving it the title of "blank" circulation. This is possibly due to the fact that the instrumental was designed for the rapping in the actual song.
Well, yeah. Though not really a harem anime, it has one guy and a bunch of girls, all of whom fall into traditional moe characterizations. In fact, some of the more observant characters make fun of it, like Oshino's habit of calling Senjogahara Tsundere.
Ironically enough, Nadeko, who's arguably the one who fits the actual definition of moe the most, turns out to be invoking and exploiting this trope.
Okay, Araragi, it's pretty despicable that Hanekawa's guardians don't give her a bedroom and force her to live in the kitchen and hallways, but this is hardly the kind of revelation that should prompt panicked hysterics...
Senjougahara's expression when she finds Hanekawa in the first episode of Monogatari Second Season. They probably were going for showing how worried Senjougahara was through an unusual amount of expression. What they made was just silly. Also while the slap was decently animated, Senjougahara's followup by pounding her fists on Hanekawa loses a lot of the intended impact because she looks like her fists are moving through molasses.
Rescued from the Scrappy Heap: Many people hated Kaiki because he was the cause of the divorce of Senjougahara's parents, without mentioning that he caused the majority of the problems in Nisemonogatari (poisoning Karen with the fire bee and selling information about Tsukihi to Kagenui) and that he indirectly caused the events of Nadeko Snake. Then Koimonogatari was released and with the reveal of his true intentions and personality and the fact that he defeats God Nadeko succesfully using only words, he turned into one of the most popular characters of the series.
Sodachi Oikura probably beat both Kaiki and the kid from Koimonogatari in the instant hatedom department. At first, she only copped heat from Ougi fans who were worried she would take screentime away from their favorite character, but following episode 3 of Owarimonogatari, where her character arc begins, there was hardly a fan who didn't despise her, mainly due to her completely unwarranted bitchy attitude towards Araragi. The hate softened a bit after Hanekawa and Araragi's visit to her house, where she's just too pitiful to hate. It helps that she took responsibility for her actions and her backstory was revealed: She probably has had the most severe Trauma Conga Line out of everyone in the cast, including outright Attempted Suicide and taking care of her mother's dead body because the death broke her that much. Marina Inoue's heartfelt monologue was a big help, and within hours of that episode's airing, the hate for her switched to sympathy and schadenfreude. In fact, it reached the point where many in the fandom poured hate on Senjougahara because she accepted Oikura's apology in a rather backhanded, arrogant manner and refused to apologize for hitting her. Nonetheless, she's still a Base-Breaking Character due to meta reasons and the fact that some fans still can't forgive her for her earlier actions, but she's getting a great deal more sympathy than she got at the beginning.
Take That, Scrappy!: Senjougahara knocking Oikura out in episode 3 of Owarimonogatari. Episode 5 shows just how much damage she did: Oikura had to stay home from school for two days and her face swelled to the point where she couldn't pronounce the "ra" syllable, which might invoke a little sympathy- although, since Oikura did spend about 15 minutes talking shit to Araragi and Senjougahara and even slapped the latter, it's hard to argue she didn't get what she deserved.
They Wasted a Perfectly Good Character: Senjougahara becomes this in the second and final seasons of the anime, as she goes Out of Focus and her status as Araragi's girlfriend is used as a plot device to cause the other girls angst rather than to further develop her or their relationship in any way.