"We are the Ultramarines, the Sons of Guilliman. Whilst we draw breath, we stand. Whilst we stand, we fight. Whilst we fight, we prevail. Nothing shall stay our wrath." — Marneus Calgar, Chapter Master of the Ultramarines
"Do not ask me to approach the battle meekly, to creep through the shadows, or to quietly slip on my foes in the dark. I am Rogal Dorn, Imperial Fist, Space Marine, Emperor's Champion. Let my enemies cower at my advance and tremble at the sight of me."
Roboute Guilliman has a cracking, cracking one at the Battle of Calth. He offered his treacherous brother Lorgar a ceasefire. It was refused. This made Roboute very angry, so he decided to channel Liam Neeson:
Lorgar of Colchis. You may consider the following. One: I entirely withdraw my previous offer of solemn ceasefire. It is cancelled, and will not be made again, to you or to any other of your motherless bastards. Two: you are no longer any brother of mine. I will find you, I will kill you, and I will hurl your toxic corpse into hell's mouth.
The Ultramarines have a cottage industry of these:
Antaro Chronus: Let them hide in their fortress. My crew could use the target practice.
Guilliman: Space Marines excel at warfare because they were designed to excel at everything.
Erikon Gaius: No brother falls forgotten.
Anciet Helveticus: A foe without honour is a foe already beaten.
Cmdr Karziel: A battle for supremacy against many foes is a battle of the best kind. There are few considerations, only those concerning where to place your next shot. It is war in its purest form.
Tylos Rubio: (*After receiving an order to retreat from the second-in-command of the entire Imperium) No, NO! You would have me leave the side of my sworn battle-brothers in their darkest hour? I refuse!...On my honour as a son of Macragge, I choose to defy it. Even if it means I will perish here, even if you colour me a rebel like Lorgar's turncoats, I defy it!
Cato Sicarius: We are the slayers of kings, the destroyers of worlds, bringers of ruination and death in all its forms. These things we do in the name of the Emperor and in the defense of Mankind. Let none stay our wrath.
Chapter Banner: Our presence remakes the past.
"Do not presume to judge me or the methods I choose to employ, petty-minded fool. You cannot comprehend the magnitude of the tasks I have undertaken, nor the consequences of my failure." — Inquisitor Lichtenstein, declared Excommunicate Traitoris 998.M41
"Some may be able to avoid the judiciaries of the Adeptus Arbites, fewer may be able to face off against the Imperial Guard and the Adeptus Astartes, but let it be known that none can stand against the Officio Assassinorum." — unattributed
"Your foe is well equipped, well-trained, battle-hardened. He believes his gods are on his side. Let him believe what he will. We have the tanks on ours." — Joachim Pfeiff, 14th Krieg Armored
"What is the strongest weapon of mankind? The god-machines of the Adeptus Mechanicus? No! The Astartes Legions? No! The tank? The lasgun? The fist? Not at all! Courage and courage alone stands above them all!" — Solar Macharius
"I am a Commissar. I am empowered to deliver justice wherever I see it lacking. I am empowered to punish cowardice. I am granted the gift of total authority to judge, in the name of the Emperor, on the field of combat." — Ibram Gaunt
"The Space Marines fear no evil, for we are fear incarnate." — Konrad Curze, Primarch of the Night Lords
"I have fought as a God fights. I am Imperius Dictatio. Kneel before me and beg for you lives!" — Princeps Ervin Hekate, commander of the Warlord-class titanImperius Dictatio
"The stars themselves once lived and died at our command, and yet you still oppose our will." — Eldar Farseer Mirehn Biellann
"Feel the rush of the wind against your skin and hear her keening cry in your ears. Listen to her call well, for are we not the Wild Riders, the children of the storm?" — Nuadhu Fireheart
"We bring only death, and leave only carrion. It is a message even a Human can understand." — Requiel, Fire Dragon
"I do not fear death. Death fears ME!" — Shas'O Sa'cea Dre'koran Ta'ar
"We own this night, just as we own the fear that runs in your veins. You may think your numbers protect you, but we shall feast upon your souls before the dawn!" — Kilarq Tongueblade, Kabal of the Lacerated Eye
"You think to challenge me, pitiful human? I, the bane of empires, the father of pain? Let me educate you; I need a new pet..." — Archon K'shaic, Kabal of the Black Lotus
"I am the hammer! I am the hate! I am the woes of daemonkind!"-Warcry of the Grey Knights Chapter.
And as for the Orks:
I'm da hand of Gork and Mork, dey sent me to rouse up da boyz to crush and kill 'cos da boyz forgot what dere 'ere for. I woz one of da boyz till da godz smashed me in da 'ead an' I 'membered dat Orks is meant to conquer and make slaves of everyfing they don't kill. I'm da profit of da Waaagh an' whole worlds burn in my boot prints. On Armour-Geddem, I led da boyz through da fire deserts and smashed da humies' metal cities to scrap. I fought Yarik, old one-eye at Tarturus, an' he fought good but we smashed iz city too. I'm death to anyfing dat walks or crawls, where I go nothin' stands in my way. We crushed da stunties on Golgotha, an' we caught old one-eye when da speed freeks blew da humies' big tanks ta bits. I let 'im go 'cause good enemies iz 'ard to find, an' Orks need enemies ta fight like they need meat ta eat an' grog ta drink. I iz more cunnin' than a grot an' more killy than a dread, da boyz dat follow me can't be beat. On Pissenah we jumped da marine-boyz an' our bosspoles was covered in da helmets we took from da dead 'uns. We burned dere port an' killed dere bosses an' left nothin' but ruins behind. I'm Warlord Ghazghkull Mag Uruk Thraka an' I speak wiv da word of da gods. We iz gonna stomp da 'ooniverse flat an' kill anyfing that fights back. We iz gonna do this coz' we're Orks an' we was made ta fight an' win! — Warlord Ghazghkull Thraka, Graffiti on Warlord Battle Titan wreckage
"Understand, mortals, that every one of you, each of your so-called champions, is just a piece in the Great Game of our Masters,"
"Slay without pity, triumph without remorse. You are the legions of Khorne, His fauvorite warriors. You shall bring defeat and death to His enemies. You shall crush their worlds under your heels. To battle! Let blood flow in His name!" — Rorath'rath the Skullweaver, daemon of Khorne
"Do not ask which creature screams in the night. Do not question who waits for you in the shadow. It is my cry that wakes you in the night, and my body that crouches in the shadow. I am Tzeentch and you are the puppet that dances to my tune." — Karantzor the Vile, the traitor of Xian.
"I am Nathaniel Garro, and I am a Legion of one"
"A Broken Sword May Still Cut"- Generic Tau Commander in Dawn of War Retribution
Also from DOW "Today We Kill A God!"- Generic Chaos Space Marines, marching to fight the Avatar of Khaine itself.
"I'm gonna stomp 'em to dust. I'm gonna grind their bones. I'm gonna burn down dere towns and cities. I'm gonna pile 'em up inna big fire and roast 'em. I'm gonna bash 'eads, break faces, and stomp on da bits dat are left. An' den I'm gonna get really mean." —Grimgor Ironhide, Black Orc Warboss
"There are no problems that cannot be solved with cannons." — Chief Engineer Boris Krauss of Nuln
"There are countless worlds beyond the void of chaos, endless kingdoms to conquer, cities to sack, forests to burn, warriors to slay in their millions. But by Khorne, I have chosen this world to conquer, and conquer it I shall, even if it takes a thousand millennia." — Khastarax, Daemon Prince of Khorne
In Werewolf The Forsaken, when a werewolf increases in Renown, they use a ritual to summon a Lune (moon spirits which serve the patron spirit of the werewolves) to brand the werewolf with a record of the deed which got them their new Renown level in glowing letters. Renown is gained by monumental achievements in Cunning (stealth, manipulation, cleverness, diplomacy), Glory (bravery, tradition, valour, daring), Honour (justice, truth, fairness), Purity (self-restraint, zeal, morality), and Wisdom (logic, intelligence, memory, intuition). This means that almost every werewolf has their Badass Boastburned into their skin for all spiritual enemies to see.
The average character in Mage: The Awakening can significantly reshape local reality on a whim, so they tend to be good at making these. In fact, making a Badass Boast is actually a ritualised part of the Duel Arcane, one of the most common ways of settling disputes between mages.
"For I walk in the Mists now and see the time that is yet to be. I will see the shadow of your coming before you have even decided your intent, and I will thwart you before you even put your pawns into motion. I will be watching from the Mists, and you will not sense it. If you move against me again, not even the Abyss and the Hidden Lords you worship will keep my hands from your neck." — Morvan, Walker in Mists
"You resist me? I, who have walked through fire without being burned? I see through your wards and unravel them with a word. Do not dare defy me." — Glorianna, Free Council Obrimos
Another Dungeons & Dragons example, according to one of the creation myths regarding the orcish god Gruumsh, it is said that after the gods finished creating the world, the patron gods of The Five Races gathered together to draw lots for where their peoples would live. The drawing was rigged, however, as they didn't have enough lots for them all and Gruumsh was excluded from the drawing. The other gods mocked that the orcs would have no place in the world, Gruumsh lifted his spear and struck it down upon the landscape, turning portions of the world harsh and barren, and declared;
"There! There is where the orcs shall dwell! There they will survive, and multiply, and grow stronger, and a day will come when they shall cover the world, and they will slay all of your collective peoples! Orcs shall inherit the world you sought to cheat me of!"
In the Dungeons & Dragons 2e supplement I, Beholder, beholders are said to enjoy telling each other stories, usually about the creatures they have killed. Such stories usually begin with a lengthy recitation of the many victories and kills attributed to the creature, ending with, "And then it met me."
Many Legendary Creatures have flavor text with either the creature's badass boast, or another person making the boast for them.
In Alara Unbroken, Nicol Bolas boasts, "I've survived more apocalypses than you've had chest colds."
When planeswalkers were godlike beings he had an even better one, it goes a good page an a half but the highlights are "I have devoured stars, and shattered worlds, I have bathed in the blood of gods, and used their bones to build my nest. I am the Mind Ripper, the deathbringer, the winged dark that terrifies your dreams. I am Nicol Bolas, Planeswalker, Elder Dragon, The oldest and most powerful being that has ever, or shall ever exist!."
Countless victories are behind us, yet we are not half done. We fight to restore a legacy once denied to us. Our enemies tremble before our invincible armies, and all will kneel or perish. The Khadric Empire is gone but the Khadoran Empire is born! - Empress Ayn Vanar.
Anyone who's been roleplaying for long enough is bound to have one or two of these.