In development of Maokai, the model for his Sapling Toss was not completed before testing him out and was instead represented by miniature versions of the current champions' models walking around and blowing up on enemies.
Ryze, the champion, was named after Ryze, the screen-name of Riot Games' CEO Brandon Beck.
Tryndamere's name started out as the screen-name of Marc Merrill, Riot Games' president and chief marketing officer.
Ezreal was named after the screen-name of one of Riot's game designers, Colt Hallam.
Volibear was named after the Rioter Volibar, who led a faction on the forums fighting for the inclusion of an armored bear.
Zilean, who dislikes Volibear in game, was named after designer Zileas, who lead the anti armored bear faction.
Udyr also shares his name with a Riot employee.
It also means "beast" in Norwegian.
Gragas's name comes from Old Norse "grágás", "Grey Goose", which is a French vodka.
On ARAM matches or matches played on the Howling Abyss, you can search for the item Guardian's Horn using the term "Golden Bicep of Kobe," referencing a showmatch $10000 ARAM played between two teams of retired pros led by Hot Shot GG and Saint Vicious. During the match, a commentator, Kobe, didn't actually recognize the item and mistook it for a "golden bicep," leading to much ribbing.
Banned in China: Similar to the issue with the Forsaken in World of Warcraft, Karthus was redesigned from a skull-faced lich to a withered, shadow-wrapped figure for the Chinese art, due to taboos about representations of skeletons in media. The only skins that keep their skull-faced appearances are his Grim Reaper skin (likely because it represents the more abstract personification of death) and his Pentakill skin (for reasons unknown).
Beam Me Up, Scotty!: Contrary to Memetic Mutation, Garen does not shout "DEMACIA!" when using Judgement (his signature Spin Attack). That's a separate skill, Courage, but because Courage is usually used in combo with Judgement, it comes across as the most widely known case.
Big Name Fan: The entire band Imagine Dragons are huge fans of League of Legends, even admitting to be late for some performances because they were playing a game. They jumped at the chance to perform Warriors live at the Season 4 World Championship.
Defictionalization: Ever want to hear Pentakill's music? Now you can with their new album, Smite and Ignite, coming out on June 3rd, 2014.
A few days before Wukong's first preview blurb, competing game Heroes of Newerth announced its new champion: the Monkey King. Technically HoN created concept art first, but didn't do anything with it until rumours about a Monkey King in LoL surfaced. Needless to say, accusations of copying were flung from both ends despite the character clearly being a reference to Sun Wukong from Journey to the West.
To begin with, we have Riot Games itself being known as "Rito Gems".
All champions with more than 5 symbols in their names have shorter nicknames for typing. Usually just first letters of the name, but any short name that clearly identifies the champion in question will do. Veigar is sometimes called Vivi, Gangplank is Pirate, and Alistar is Cow.
Acronym nicknames are also common in order to shorten some character names for ease in writing on forums or chats. Gangplank is 'GP', Miss Fortune is 'MF', Jarvan IV is 'J4', LeBlanc is 'LB'. Master Yi seems to be an exception because he can simply be called 'Yi'. LAN also has Kha'Zix being known as 'K6' due to the "Kha" being pronounced in Spanish as the letter K.
Items also have their acronyms, such as BotRK (Blade of the Ruined King), IE (Infinity Edge), PD (Phantom Dancer) and DFG (Deathfire Grasp).
Items in LAN are often known by their NA names, due largely to the early days of LOL when Mexicans had to play in NA. This makes it rather hard for a LAN native to receive advice from a NA immigrant as they tell him to rush IE and PD or a DFG instead of "Filo del Infinito" and "Bailarín Espectral" or a "Garra de la Muerte Ígnea".
Certain champs get their perceived overpoweredness reflected with a spin on their name. For example, Win Nao the Senechal of Demacia, Master GG, Free Win the Blind Monk, Gankplank, and Feed-lesticks.
The same happens when a champion gets hit too hard by balancing adjustments. This is how Kassadin became "Nerfadin".
Second accounts are called "smurfs" (more or less officially, as Pendragon himself has one and calls it a smurf too).
This one extends outside of LoL.
The new Proving Grounds map has been affectionately nicknamed 'Murderbridge', due to the fact that its a bridge upon which lots of killing happens. Of course, it is also actually what the file for the map is called.
The Rated M for Manly champions Pantheon and Jarvan IV are affectionately nicknamed Mantheon and Jarman respectively.
Malzahar's Malefic Visions attack, due to the fact it spreads like a virus after killing the original target and because of the general spacey theme of the Void, it is often called "Space AIDS".
Most people know you're referring to Master Yi with the name "Samurai Fisher" due to his goggles having the similar glow effect.
Due to this "pro as heck guide to master yi", Master Yi is commonly nicknamed Dunkmaster Yi. Jarvan IV and Darius have also had the title Dunkmaster bestowed upon them by the fanbase as the animations for casting their ultimates resemble a one-handed and two-handed dunk respectively. In fact, it's become an Ascended Meme with the Dunkmaster Darius skin.
Vladimir's Sanguine Pool is an ability frequently used as an escape. Due to its ability to make Vladimir untargetable to things that are not already homing in on him while also speeding him, it gained infamy for its ability to completely save Vladimir at the last second or let Vladimir not help allies in need despite appearing to and was dubbed "Trollpool".
Fizz's Playful/Trickster abilities makes Sanguine Pool looks like it needs supplements when directly comparing escape abilities. Playful immediately makes Fizz hop on top of his trident to be invulnerable and untargetable to anything up to a very short duration and lets him cast Trickster which then has him jump away onto a nearby location - such as over walls. And place your allies back into impending doom, naturally. Needless to say, it did not take long for it to be known as the "Trollpole".
Kayle has been referred to as Samus, due to her similar design, similar Knight Templar attitude, and the fact that a limited edition skin exists that does nothing but take her helmet off.
Even during season 3 when Riot switched to a "3.x" naming convention for their updates, it still is common for patches to be named after the champion they introduce (Thresh patch, Lucian patch, Yasuo patch, etc.). The big exception, of course, was patch 4.20.
Aatrox and (formerly) Thresh are often known as "Anthrax" and "Trash," respectively, among Dominion players due to them occupying the bottom-most tier within the Dominion metagame. Thresh has since been buffed and sits in the middle of most top-lane tier lists and fairly high on bot-lane tier lists.
Garen is often referred as 'Bushren', since one of his 'common' tactic is to hide in the bush and then strike at any poor schmuck that dared approach his bush.
Mordekaiser is also associated with nicknames like 'Mordhuekaiser' or 'Huekaiser' or any variations that inserts 'hue' on his name thanks to the Brazillian-related meme of "Mordekaiser es #1. HUEHUEHUEHUEHUEHUEHUE"
Sometimes, Teemo is referred as Satan or Shitrat. The latter is particularly hilarious when you remember that Twitch is a champion.
"Helmet Bro": The nameless knight dude who is usually a victim of a champion's badassery in either their promo or splash art.
The original voice actress for Karma was Danielle McRae, who happened to be the voice actress of Painwheel. Unfortunately, when Riot decided to rework Karma in terms of gameplay and graphics, they replaced her with a different voice actress, but they kept Danielle's voice work of Karma for the "traditional" skin.
Ziggs and Rumble are voiced by none other than InvaderZIM and Raz.
One of Us: If this Rammus Taunts Everyone video is any indication, Adam Harrington (Mordekaiser, Ryze, Shaco, Kassadin) may be one, as he is aware of the memes of League and even voiced Mordekaiser there while saying "Huehuehuehue". Yes, we're not kidding, the REAL Mordekaiser saying "Huehuehuehue". Aside of that, he's VERY active in the youtube community of LOL.
Same goes to his buddy Erik Braa (Jax, Draven, Vel'Koz)
Riot then released this "spotlight". Game Breaking... no, Game DESTROYING power, a "blurry" screen debuff, and the ability to kill members of your own team who defect to the other side. They released an actual spotlight video shortly after.
Their 2012 prank (a really bad 3D mode) was obvious (made even more so by the Urf cameo at the end), but nonetheless hilarious. Incidentally, they've actually named April Fool's Day "Urf Day."
Riven was originally pitched as "Gooder than good"according to her designer Xypherous. She also had an alternate backstory about her being an exile from Demacia, which was changed just before release. This is the reason for the Redeemed Riven skin, which was released with her on launch but looks notably Demacian and seems unfitting both in appearance and name-wise to her current backstory.
Xypherous originally intended Nautilus to have an ultimate that involved picking up an enemy champion and spinning them around him. It, regrettably, simply did not pan out. He also wanted Nautilus to have a base movement speed even lower than the bottom-of-the-barrel 300 Nautilus has right now, but said they wouldn't let him make it any lower.
Wukong's kit was originally completely different, and stated to be very complex.
When Riot gave people a boost to get a Corki skin and reduced it in price...the people who missed it screamed so loudly they've since been very careful about that.
The developers don't often post in the forums because the average post is usually about as negative as the temperature in Antarctica.
Recently, a code to get a free skin for Caitlyn as well as the champion if you didn't already have her was put in the November issue of PC Gamer. A lot of people are reporting that people are going into stores and copying down codes printed in the magazine so they didn't have to pay for them. Several people have predicted that they won't be doing this anymore, even though PC Gameris combating this by having people email or call in with a proof of purchase to get another code.
More recently, when Annie's visual update was ready to be patched in, Riot announced that they'd release the Goth Annie skin for a limited time for players to buy who didn't purchase the Champion bundle it's normally exclusive to. This resulted in a massive outcry from players who valued the exclusivity of the skin, causing Riot to promptly retract the offer. Riot is now considering alternatives to such offers, but those who were looking forward to buying Goth Annie are going to have to keep waiting to complete their collections.
Trope Pantheons: Several champions attained their place in the Pantheons. And true to their rivalry with Dota 2, all of the champions list the Dota heroes as their rivals. Not that it stops some of them sharing one house.