There is a skill for the Mechromancer called "20% Cooler" This is a Reference to the TV Series "My Little Pony: Friendship is Magic" where the character "Rainbow Dash" says "It needs to be about 20% Cooler".

Spoiler:After Mordecai shoots Bloodwing with a tranquilizer dart at the end of her boss fight, it is possible to shoot her after she falls to the ground. Even though she is defeated, every shot fired at her head will still count as critical hits in your Badass Ranks.

During a second playthrough on "True Vault Hunter Mode", after the chapter "Where Angels Fear to Tread", the player can go to Claptraps Place and find an event item in the fireplace called "Geary's Unbreakable Gear" with the description "Only a brisk walk to Eridium Blight will reward the courier". The player must then travel to Mount Hellsfont, located in the northwest corner of Eridium Blight without dying, using a fast-travel station, or riding in a vehicle spawned from a "Catch-A-Ride" station. If the player is successful, they'll encounter a special enemy named Geary. If the player lets Geary attack them, he'll steal the gear and jump into the lava. This will cause three Rakks to appear and drop three loot chests, one of which will have purple gear. This is a reference to "The Lord of the Rings" book trilogy by J.R.R Tolkien, and the journey to Mount Doom.

The Baby Maker SMG explodes into two smaller versions of itself when reloaded. The chances of spawning a pink or blue variation are actually based on US birth statistics for females and males.

Mister Torgue is censored by a device in his voicebox, rather than being edited later. In his own words:

The red flavor text for the Buffalo gun refers to three notable linguistic constructions:
a sentence that uses the word "buffalo" 9 times and is still grammatically correct, a sentence that repeats the word "had" 11 times to illustrate the importance of punctuation, and a Chinese poem that tells a story using a total of 92 words, which are all pronounced in varying tones of "Shi".

The commando for Borderlands 2, Axton, has been confirmed as bisexual by lead writer Anthony Burch.

The "these pretzels suck" and Butt Stallion dialogue spoken by Handsome Jack were ad-libbed by voice actor Dameon Clarke. Writer Anthony Burch was upset that these became Handsome Jack's most popular lines as he had no hand in writing them.

There is a Shotgun in the game called 'Dog'. In the game's code, its file name is "Thre Dog", and its special weapons effect reads, "Because one barrel ain't enough, and two is too few." This is likely a reference to the character "Three Dog" from Fallout 3, who says "Three Dog, because one dog ain't enough and two is too low, it's Three Dog!"

In Sanctuary, there is a chance that an NPC will say "I used to be a Vault Hunter like you, until I took a bullet to the knee." This is a reference to the infamous "I took an arrow in the knee" meme from The Elder Scrolls V: Skyrim.

Tiny Tina's lazy eye is actually a bug in the software. Instead of fixing her eye tracking, the developers thought that it fit with her character, so they decided to leave it in the game.

There is a side mission in the Tiny Tina DLC called "Lost Souls." In the mission, the player helps an undead warrior by collecting souls at camp fires, just like in Dark Souls.

The mission title "Hungry like the Skag" refers to a Duran Duran song, Hungry Like the Wolf, as Skags are wolf/dog-like creatures in the game.

In the Hammerlock DLC there is a side quest "The Rack Dahlia Murder". The mission title is a reference to the unsolved 1947 Black Dahlia murder that occurred in California.

There is a unique relic in the game called the "Deputy's Badge" which is awarded for finishing the mission "The Showdown". Part of its description reads "Who the hell shot me?", a reference to the Bob Marley song "I Shot The Sheriff", the chorus for which begins with "I shot the sheriff, but I did not shoot the deputy."

In the mission Assassinate the Assassins, the Assassins are called "Wot", "Reeth", "Rouf" and "Oney". "Wot", "Reeth" and "Rouf" are anagrams of "Two", "Three" and "Four" while "Oney" is just "one" with a "y" on the end.

The skin "Vault Dweller" for the Siren is a reference to the outfits worn by the members of the vaults from the Fallout series. It follows its color pattern with blue body and yellow highlights.

In the Caustic Caverns, across the acid water, there is a small island with a Knight named Solitaire sitting on a ledge in front of a bonfire. White phantoms are also sitting in front of the bonfire. This is a reference to Dark Souls, with Solitaire being a reference to the knight Solaire of Astora.

While fighting enemies as Axton, he may say "And YOU get a bullet, and YOU get a bullet! EVERYONE gets a bullet!" - a reference to Oprah Winfrey's energetic nature and giving audience members gifts.

There is an enemy called "King Mong", an homage to King Kong, that can be found in the game.