Colbert Bump: Originally intended to be a niche game catering mostly to the military otaku population with a modest budget and minimal advertisement, its popularity experienced a huge surge after its players (including, among others, KohtaHirano, whose Heroic BSOD on twitter is most commonly cited as the main reason for the popularity surge) spread the word on Twitter and/or Pixiv.
"Beaver" for Yukikaze, due to how her top teeth are drawn in her character art.
"Henderson-chan" among Western players for the Airfield Princess, That One Boss of the Fall 2013 event, due to her being based on the real-life Henderson Field at Guadalcanal.
"Darwin-chan" for the Seaport Princess, and "Wake-chan" for the Isolated Island Demon. Following the example of the Airport Princess, their nicknames reference the real-world places (which were the locations of Allied bases) they're representing: Port Darwin in Australia, and Wake Island, respectively.
Seaport Princess earned the additional nickname of "Oppai" for having the largest bust in the entire Abyssal Fleet.
Many have taken to called Nothern Ocean Princess "Hoppo-chan". Western players on the other hand, have started calling her "Mittens".
"KTKM-sama" for Torpedo Cruiser Kitakami; the nickname itself is obviously just her name with all the vowels taken off, while the respectful "-sama" is due to the fact that many endgame fleet compositions pretty much require Kitakami (or Ooi, or both of them) to work.
"Tenryuu's Kindergarten", for any fleet composed of light cruiser Tenryuu supported by a gaggle of destroyers (who, like Hibiki and her sisters, are drawn like kids). Supported by the official 4koma, which mentions that Tenryuu is apparently good with kids. Because of her low maintenance cost, she is frequently used in expeditions along with destroyers, and both official 4koma and fanworks reflect this trait.
Apparently Bushiroad has caught onto this and given Tenryuu a skill of gaining power for each Level 0 character on the field in the Weiss Schwarz TCG.
"Mom" for Houshou. In-game due to her gentle tone of voice, and the fact that she has one of the lowest maintenance costs of any carrier. Much like Tenryuu, this makes her ideal for "babysitting" the kids/destroyers.
Houshou is also the first aircraft carrier of the world to be designed to be a carrier and finished, making her the mother of all carriers (which is also a tag dedicated to her alone). note The first converted aircraft carrier, as well as the first designed aircraft carriers, goes to the Brits with Battleships.
"Nagamon" for Nagato. When you see this being mentioned in fan art, you're guaranteed to see her cuter/sillier side being depicted in them.
12-suzu or 十二鈴 for Isuzu, both being a play on her name and the fact that she remodels at level 12, tying in with the Isuzu Farms entry in Memetic Mutation.
"Poi" for Yuudachi. This usually refers to her Kai 2 form, which is arguably the most useful destroyer in most situations where you wouldn't otherwise use one, due to her firepower being on par with a heavy cruiser's.
Anything perceived to be a common result from anything, be it drops from nodes or results from crafts, will be termed the "Naka-chan" of that node or craft, due to her ridiculous ubiquity in normal ship crafting. For example, Maruyu is the Naka-chan of large ship construction.
And with the addition of I-19 into the roster, her lines towards the player plus the pronunciation method to her name (Iku), as well as the way she talks, has caused some people to, er, do a double take on it - which led to her getting her own tag in Pixiv, named "Oyogu Juu-hachi Kin" (Swimming Adult Content, for lack of a better word). note In case you haven't noticed why, I-19 pronounces and spells her name as "i-ku". Guess from what else you might hear these two syllables get used so often...
"Seal"' for Shimakaze, for her surprised "Au!" reaction. Also Zekamashi, from the kana on the life buoy she's sometimes seen with.
Bismarck is sometimes called "Biscuit" or "Biscuit-chan".
"Raiden" for Ikazuchi and Inazuma together. Brought about by how the word is made up by the kanji from Inazuma and Ikazuchi's names.
"Yaggy", used to collectively refer to Kagerou, Kuroshio, and Shiranui. Comes from a compression of the characters used in their introductory lines and is used in reference to attempts to build Yukikaze (who has the same build time, being of the same class as these three but is much more rare than them).
"Oreal Cruising", which refers to using a team of subs to farm world 2-3 for fuel and ammo, as well as completing daily and weekly quests on the side.
Kuso teitoku/"Shitty admirals", for the clueless posters that could be found everywhere on the English wiki for the game. Taken from Akebono's in-game nickname for the admiral, the term is used to describe the (usually anonymous) posters who clog up the Recent Updates or Event pages with their posts, usually with questions whose answers should be readily found on the wiki to begin with, whining about how maps, event or otherwise, are "too hard" (despite the fact that advice on how to clear said maps is also on the wiki itself), or worst of all, posts about reckless or apathetic behavior (like not caring whether their ships get sunk, mostly due to their own stupidity). Essentially the Kantai Collection equivalent of Frodos from 4chan, or Tomatoes from World of Tanks, and equally looked-down on by more sensible players.
Some people would also use this derogatory nickname for admirals putting low-level shipgirls on the first and second slots of their first fleet then fill the rest with high-level shipsnote The EXP gain for PvP battles are calculated largely on the level of the opponent's flagship and second ship. With this configuration, opponent fleets are denied ship EXP while still having a good chance of being defeated, just to deny experience for other admirals in player-versus-player side of the gamenote a significant source of EXP for ships, with MVP gains of around one to two thousand points for one battle.
"Black Wock Shooter": Wo-Class Kai Flagship has a blue flame on her left eye. Other remodeled flagshipsnote the distinctive blue eye-flame is most pronounced on them following this theme have spawned following the Spring 2014 event (usually Ri- and Ru-classes). The general drawing style of humanoid Shinkaisei-kan are also quite reminiscent of huke's style in BRS.
Fusou and Yamashiro are known as the "Unlucky Sisters".
Hey, It's That Voice!: All ship girls are voiced by well known voice actresses from the anime industry, including but not limited to:
Irony as She Is Cast: Sumire Uesaka is well known as a Russophile, yet the role of Verniy is (assumed to be) given to Aya Suzaki. If Sumire were to actually get the Hibiki role, we may be showered with more Gratuitous Russian lines, and that may end up as a sweet reward to her fans for putting hard work in leveling her up to 70.
The official 4koma has Fubuki (whom Sumire Uesaka voiced) communicating with the suddenly-converted Verniy (Hibiki's second remodel) with (supposedly) good Russian, only to reveal that Verniy cannot really speak Russian apart from rudimentary words.
No Export for You: The only way to play the game is to register on the Japanese-language segment of the DMM website, which itself is inaccessible to non-Japanese IP addresses. This means to even register for the game, a prospective non-Japanese player will have to jump through a lot of hoops to do so (usually by using VPN), nevermind getting to play the game, which then requires newly-registered members to win a lottery for one of the limited slots per server. And competition is steep for server slots.
The January 29, 2014 update was a rude awakening for many foreign players, as the most prevalent method used to play the game (the API link) no longer worked, since DMM had the game purge its API lists every 90 minutes. This meant that anyone who wanted to play via API was now essentially playing on a timer, and they had to hop on VPN to renew their API link when the time was "up". The other choices were playing on the VPN full-time, which carried its own associated risk, mainly a chance of getting banned for using a single IP (as DMM would technically see a single IP used by multiple accounts), or purchasing a private VPN to play the game on. In any case, this caused a lot of grief for non-Japanese players, causing some of them to drop the game outright rather than face the hassle of renewing every hour and a half. However, said API renewal forced a lot of players to log in simultaneously, overloading DMM's log-in servers, and essentially making the game inaccessible to everyone for hours on end. It was quietly removed in a subsequent update.
However, API links is no longer a concern. A not-so-recent method involving cookie editing allows any foreign player to play the game properly.