Insult of Endearment

Two people really don't get along. To show how well they don't get along, one of them gives the other an insulting nickname and refuses to call them anything else. However, over time, the nickname really doesn't become that insulting anymore, and as the characters learn to respect, if not like, each other, the formerly insulting nickname actually becomes more a term of endearment.

This trope is a good way to show Character Development. As two people who initially disliked each other grow closer, the use of a formerly insulting nickname as a gesture of affection is a good way to showcase their evolving relationship. The Vitriolic Best Buds may see insulting nicknames as just part of their snarky banter rather then something genuinely meant to hurt, and couples who use insulting nicknames as part of their Belligerent Sexual Tension may soften the use over time to show that They Really Do Love Each Other.

Not to be confused with Insult Backfire, when an insult is taken as a compliment, or Appropriated Appellation, when the person cleverly uses the insulting name to his/her own advantage. In order for it to be this trope, the original nicknamer has to change from using the name as a deliberate insult to using it as a term of endearment, or at least friendly ribbing. Contrast Terms of Endangerment, where a villain addresses a hero by an affectionate name but there's nothing behind it but hatred.

Because this trope typically accompanies Character Development, there may be unmarked spoilers present. -

Anime And Manga

 * Boku wa Tomodachi ga Sukunai: Yozora refers to Sena as "Meat" because of her Gag Boobs. It becomes clear later on that the nickname isn't really an insult anymore, and Sena actually secretly likes it because it's the first time anyone gave her a nickname.
 *  Toradora!: Taiga calls Ami "stupid chihuahua" ("baka-chi") at first, but after both go through a lot of Character Development, it seems to be more of just an habitual nickname than a deliberate insult.
 * Tiger and Bunny: Veteran superhero Kotetsu resents having to team up with rookie Barnaby, due to the latter being younger, better-looking, more beloved of the sponsors, and having the exact same powers as him. He gives Barnaby the insulting moniker "Bunny-chan" as a pun on his given name. Later on they start acting like real partners, and "Bunny" becomes Kotetsu's personal nickname for his partner. Barnaby, who used to take offence at being called by the the nick, eventually comes to accept it...though he still won't stand for being addressed as "Bunny-chan".
 * Sailor Moon: Mamoru creates the insulting nickname "Dumpling Head" (Odango Atama in Japanese, Meatball Head in the English Dub) for Usagi, but it later on becomes a term of endearment after they fall in love.
 * Lovely Complex: Vitriolic Best Buds Koizumi and Otani refer to each other as "midget" and "amazon" or "totem pole" respectively. Later, after the, they still occasionally call each other this, though in a considerably softer manner than before.
 * Takeda "The Puncher" and Kozo "The Thrower" manage to use their monikers very touchingly in the dub of Kenichi: The Mightiest Disciple after both complete their Heel Face Turn (s) (managing to save Kenichi (for both), save Takeda and Kenichi (for Kozo)), and both upright quitting Ragnarok, reaffirming their friendship and promising to help each other out. Prior to this, their monikers were being used rather beratingly by their superiors.
 * Naruto calls Jiraiya "Ero-sennin" (pervy hermit) throughout the story but it's clearly not insulting anymore after the Time Skip, and even less
 * Also, Sasuke calls Naruto "usuratonkachi" in canon, which essentially means "idiot." It's claimed in the Official Databook that Sasuke has began using it as a "pet name" or "in an affectionate way".
 * In Majin Tantei Nougami Neuro, Neuro frequently calls his human assistants "servant number one" and "servant number two" (along with a lot more one-off insults). By the end of the series, though, he develops a sort of demonic respect for the human Yako, and "servant" becomes if not affectionate, then at least respectful. He maintains that Yako is still a "pillbug"... but the rest of humanity are amoebas by comparison.
 * In Pandora Hearts Gil calls Alice "Baka-usagi" and Alice calls Gil "Seaweed head" noticeably even after they become closer.

Comic Books

 * In Transmetropolitan, Spider Jerusalem, Intrepid Reporter and all around Anti-Hero resents the two assistants foisted upon him by his editor, so he dubs them the "filthy assistants." Later on, after he starts respecting them, "Filthy Assistants! To me!" practically becomes a Catch Phrase.
 * Lois Lane's use of "Smallville" for Clark Kent in some continuities goes from insulting to affectionate over the course of time.
 * The Incredible Hulk tends to do this with his enemies-who-become-friends when in his Hulk Speak mode. Examples:
 * Doctor Strange: Dumb Magician
 * Prince Namor the Sub-Mariner: Fish-Man
 * Spider-Man: Bug Man
 * Nighthawk: Bird-Nose
 * Iceman: Ice Man...OhWait
 * In the Archie Sonic the Hedgehog comics, Antoine is often referred to as "Ant" by the other Freedom Fighters, as an insult as first (i.e. comparing him to an ant) but later as a friendly nickname.

Film

 * In National Lampoon's Animal House, plump and naive Kent Dorfman, the newest member of the Delta house is given the nickname "Flounder", probably because of his size(in comparison to fish maybe), yet this becomes an endearing name for him over time.

Literature

 * In the novel Terminal World by Alastair Reynolds, the main character is a doctor named Quillon. He's accompanied by a guide named Meroka. She doesn't like doctors, and at first, doesn't particular like Quillon either, so she insists on always calling him "Cutter", much to Quillon's chagrin. However, as the novel progresses, Meroka begins to warm to Quillon. She still calls him Cutter though.
 * Amusingly, even other characters begin calling him Cutter, as they mistake that for his real name due to Meroka's continued use of it.
 * "Princess" was used as a mostly pejorative nickname for  in Deadline, but it became slightly affectionate toward the end of the book.
 * Early in the first book of A Song of Ice and Fire, Jon is given the nickname "Lord Snow", to emphasize his illegitimate birth. As everyone hated him when he first arrived, no one used it affectionately. Later, though, he started to gain a lot of friends, and toward the end of the third book many people use "Lord Snow" as a term of respect, although the person who originally coined it still meant it as an insult. Eventually,.
 * In the Descent novels, Sierra Taurus addresses Ben St. John with the nickname "Little Bird". This grates on St. John's nerves (like Taurus wanted), but after they complete their first mission together and become true wingmates, he keeps using the term and St. John doesn't mind it. It becomes so common between the two of them that realizes St. John has survived in the third book because someone overheard Taurus address him that way.

Live Action TV

 * Bones: Hodgins dismissivly calls new intern Finn Abernathy "Opie," after the character in The Andy Griffith Show. Abernathy counters by calling Hodgins "Thurston." By the end of the episode they've gained respect for each other, but still use the same nicknames.
 * Played With by Booth and Bones herself. Booth originally used the name as a term of endearment and respect for Brenan but  he continued to call her it out of a desire to annoy her and always got a "Don't call me Bones!" in response. Later on she came to like the nickname again and he became the only person allowed to call her that.
 * Scrubs:
 * J.D. is initially called "Bambi" by nurse Carla, as he's a new and inexperienced doctor. The nickname persists even after J.D. becomes more experienced and Carla becomes friends with him.
 * Dr. Cox definitely meant his terms for the main characters ("Newbie"/, "Barbie" and "Ghandi") to be insulting, but kept using them even once he started to respect them as doctors.
 * Doctor Who: As he departs to fight the cyber menace in a world not quite his own, the Doctor fondly calls him "Mickey the Idiot" one last time.
 * During the 7th Doctor's run, rebellious teenager companion Ace called the Doctor "Professor" to annoy him as part of her anti-authority streak. It later turned into an affectionate nickname between them.
 * In Nikita, Nikita often calls computer supergenius Berkoff 'nerd'. It started as her way of insulting him but as they worked together they became friends so now it is her way of showing him affection. She is the only one he allows to call him that.
 * In a BBC production of Gaudy Night, when Peter proposes to Harriet near the end, she responds, "Dear Idiot!" and then kisses him. Although this is different than the novel's depiction (in which he proposes and she accepts in Latin), according to canon they've had several years of BST up to this point.
 * CSI: NY Danny's calling Lindsay "Montana" start out this way; they never hated each other per se, but he used it to tease and annoy her, and it turned into a pet name later on.

Video Games
"Rita: (condescending) "Not bad for a dog!" changes to: Rita: (admirably) "Good job, Spot." then finally: Rita: "Nice job, Repede!""
 * In Final Fantasy VII, Barret continues to call Cloud "Spiky" as a derogatory referral to his hair, but by the end of the game, it has become a term of endearment.
 * In Dragon Age II, the prim-and-proper Aveline keeps calling the Pirate Girl Isabela "whore", at first with disdain (though Isabela doesn't mind the moniker) but as the two women come to know and accept each other, "whore" becomes Aveline's term of affection of sorts for Isabela, which she now actively enjoys from her.
 * The werewolf in the Dark Brotherhood in Skyrim constantly refers to you as "hamshank" and various other nicknames for food. He explains that as a werewolf, you look awfully appetizing, so he's going to call you food. He warms up later... as far as sociopaths "warm up".
 * In the Nijiiro no Seishun canon of the Tokimeki Memorial Drama Series, Minori Akiho calls the main protagonist "Juu-rokuban no Senpai" (No.16-Senpai, referring to his shirt's number in the Soccer Club): the nickname had a derogative connotation at first due to the intense jealousy she had towards him for getting her beloved senpai Saki's attention, then after her Character Development kicked in and she came to like him, it becomes an affectionate nickname.
 * Tales of Vesperia: Rita Mordio. If used with Repede, she first refers to him as "dog". If you continue to use them together, she starts to warm up to him and affectionately calls him, Spot, instead. By game's end, she calls him by his own name. Basically going from:

Western Animation
"Katara: You've been training for this since the day we've met. I've seen your progress. You're smart, brave, and strong enough. Aang: You really think so‌? Sokka: We all do. You can do this. You're ready. Toph: You're the man, Twinkle-toes!"
 * Avatar: The Last Airbender, during the "Blind Bandit" episode, Aang manages to sneak onto the Bei Fong family's estate, without alerting the guards, to ask Toph to be his earthbending master; which leads her to call him "twinkle toes". As the series progresses, what began as an insult starts to become more of a nickname, and finally a term of affection, as seen at the end of "Nightmares And Daydreams".


 * King of the Hill kind of uses this: Cotton always referred to Peggy as "Hank's Wife," which demonstrated both his sexism and his general dislike for her. However, in later seasons he even uses it when he's trying to be nice. It's worth noting that his Character Development also includes indications that he's at least a little bit senile.