Kouji (Great Mazinger manga): Grandpa's murder... All the people who have been hurt... Japan's peace trampled... All because of Dr. Hell... this time, for sure... This time I'll destroy Dr. Hell for good!
Dr. Hell (in reply to the boast above): Destroy me... Is that so...? A Mazinger Corps...? You mean to say that you've raised up all the might of your country to destroy me? How much pretentious... What clever leadership you must have... However, it seems the "little island country" has gotten a swelled head. To try and keep Dr. Hell from becoming ruler of the world...? Well, that's just fine! My conquest of the world will begin with Japan! I'll show them! I'll destroy Japan in a mere ten days! And the world shall know the true power of Dr. Hell!
Great General of Darkness (during his climatic duel with Tetsuya in the Gosaku Ota manga): "Your end has come! I have already failed too many times with you! For your blame, the Emperor of Darkness has got a fit of rage! Now I am through playing with you! The strength of the General of Darkness, commander of seven armies of Mykene… Now it shall descend upon you!"
Emperor Vega (UFO Robo Grendizer anime): I am Vega, Emperor of Universe and I command you submit to me!
Dr. Hell (Mazinkaiser): At last! The time has come... for my troops and me claiming our Empire!
Tetsuya (Mazinkaiser): Damned Beasts! I will make you to pay for what you have done to the Institute!
And in Mazinkaiser Kouji and Tetsuya got the next exchange:
Kouji: Very well. I'll deal with the Mechanical Beasts.
Tetsuya: Kabuto! Go and strike Dr. Hell's base.
Kouji: Do you think you can defeat them without help?
Tetsuya: Of course! My robot is a Mazinger right like Mazinkaiser!
And in the Shin Mazinger Zero manga, Mazinger was chained and immobilized by a Mechanical Beast as another was trying to impale it:
Kouji: But... I won't lose! Mazinger Z will definitely not lose!
Fiamma: I'm about to save this world. Therefore, I have no more use for you. Feel the glory, meatbag. Your value as a human being, obediently let me have it.
When first rescuing Index:
Touma: God, if the world really goes by your rules, then I'm gonna smash that illusion apart!
In the rematch with Accelerator :
Touma: Does a Level 0 like me really seem that incredible?! Hero? Villain? Stop kidding around! Can’t you save someone if you’re not standing at that spot?! In front of your eyes are people that don’t wish to cry that are crying! In front of your eyes are people that can only clench their teeth while struggling and can’t even say the words ‘please save me’! Is that not enough!! Just step up already!! You don’t need special positions or reasons!! With these, you can step up and be a shield for them!!
Touma's response to one of Fiamma's boasts:
Touma: Our world is not so weak that it needs to be saved by a bastard like that.
Heaven Canceler may be an Actual Pacifist doctor, but even he can have one.
Heaven Canceler: Well, just don't die. As long as you don't die, I can fix you.
Kyon from Haruhi Suzumiya. You've gotta hand it to him. In the 1st book, Melancholy, he nearly got killed by Ryoko. In the 4th book, after nearly being killed by her a second time due to a humongous in-universe Retcon, he threatens the Integrated Data Sentient Entity into not deleting Yuki. This is the IDSE, who's nothing but data, and cannot be detected. Kyon threatens it by convincing it that he can provoke Haruhi by saying that he is John Smith. It works. Let us reiterate. He tells a superintelligent alien god to back down. And it does. "If anything happens to Yuki Nagato, I will unleash hell."
Rosette delivers one in the first chapter and episode of Chrono Crusade:
Manga: "Send peace to those who are lost! "Send rest to those who threatens others! "And send death to the demon! "GOSPEL!"
Anime: "Bring peace to the lost lambs, "Give rest to the fangs of wolves, "And call the hammer of death unto the devil!"
Parodied in Gundam 00. Patrick Colasour in the 1st episode claims to be unbeatable throughout 200 simulation battles in front of The Stoic Setsuna, only to be easily cut down by the latter. And he spends the rest of his lifetime being Team Patrick.
Specifically, he gets cut down while boasting. The attacks do not stop his mouth. He finishes just before he hits the ground.
He repeats this throughout the show in almost every appearance, still being either defeated before or just after he finishes his boast and/or promises a win to his commanding officer.
"Throughout the sea, men speak of my strength, greater than any living man. A vast crew of eight thousand men follow at my back! Know fear, for I am CAPTAIN USOPP!": A subversion from noted liar and coward Usopp.
"I travel the seas of the world, obliterating every enemy in my path. I can't count how many ships I've sunk. People fearfully call me Lord of Destruction. Remember my name well. CAPTAIN USOPP!" He's rather fond of this trope
Later on, he develops his own theme song and a Superhero identity to go with it named Soge King.
And yet, stories he told Kaiya during his introduction, such as fighting a giant woman, have happened. Maybe it's not so much a boast as a prediction.
Don't forget the giant goldfish that he claimed to have followed around the seas—only to encounter one when leaving Little Garden.
Post-timeskip, he notes how far he's come. "I've really degraded as a liar. Now, I can actually do these things!"
Ahem: I AM WHITEBEARD!
No description needed. Just his name. And if you don't believe it... Well, here's when he made the boast. And remember, not only was he already wounded due to a cheapshot and terminally ill, he was still holding back.
Even Luffy has done this. "There is no one in the world who can beat me, because I am a rubberman!"
At Thriller Bark: In response to "The nail that sticks up gets hammered down": "No one can hammer me down, because I'm a rubber man!"
Even better in the English translation.
Moria:The nail that sticks up is always pounded down!
Luffy: I'll never be pounded down
Moria: Won't be pounded down? You're naive, kid.
Luffy: Rubber always bounces back.
At Enies Lobby: "We have ten thousand men guarding this island! This is the greatest fortress of justice in the world!". "Yeah, and I'm alone, so GET OUTTA MY WAY!"
And there's a lot more where that came from, too numerous to list.
"Listen up, Straw Hat Luffy-senpai is the one who will one day take on this era! The future pirate king." By Bartolomeo.
Lest we forget THE definitive badass boast of the whole series:
Luffy: I'M GONNA BE KING OF THE PIRATES!
This boast is so badass it can momentarily stop an all out war.
Luffy gives one to Lucci after he's just collapsed for the first and, by definition of the boast, last time.
"Until I defeat you...I won't drop to the ground...ever again."
In Princess Mononoke, Eboshi has many qualities of a Lady, but humility is not among them. Which she makes perfectly clear when she accusses the emperors own elite soldiers of being cowards during the final showdown.
Now watch closely, everyone. I'm going to show you how to kill a god. A god of life and death. The trick is not to fear him.
Kamina: "I'm going to tell you something important now, so you better dig the wax out of those huge ears of yours and listen close! The reputation of Team Gurren echoes far and wide. When they talk about its badass leader - the man of indomitable spirit and masculinity - they're talking about me, the mighty Kamina!"
Then the combining of Gurren with Lagann to create one of the titular mechs...
Kamina: You'd best remember this, you fuzzball! Combining is all about one man's fighting spirit slamming into another! Setting a man's soul on fire! COURAGE COMBINING, GURREN LAGANN!JUST WHO THE HELL DO YOU THINK I AM?!
Simon also becomes quite skilled at it, too. As in spending the last episodes with ALL his lines being of that kind. While fighting god-like enemies.
He gives an excellent one during the definitive He's Back moment of the anime.
Simon: "My bro is dead. He's gone! But he's right there on my back, and here in my heart! He lives on as a part of me! If you're gonna dig, dig to the heavens. No matter what's in my way, I won't stop! Once I've dug through - it means that I've won! ... Just who the hell do you think I am? I'm Simon. I'm not my Bro! I'M ME! Simon the Digger!"
Hell, almost everybody in the show does this before (and sometimes during) a big fight, usually ending with some variation of the infamous Catch Phrase. Every single time it's a Crowning Moment Of Awesome - and often a Crowning Moment of Funny - and each one more awesome than the last. Heck, there's even a multi-person Badass Boast in the final episode. And it is sweeeeeet.
Simon: Don't underestimate us! We don't care about time, or space, or multi-dimensional whatevers... We don't give a damn about that! Force your way down a path you choose to take and do it all yourself. That's the way Team Dai-Gurren Rolls!
Anti-Spirals: How... how can this be? WHERE ARE YOU DRAWING ALL OF THIS POWER?!
Simon: We evolve... beyond the person we were a minute before! Little by little... we advance a bit further with each turn! That's how a drill works!
Anti-Spirals: That's the path that leads to extinction! Why can't you see the pathetic limitations of the Spiral Race?
Simon: No, that's YOUR limitation! You sit here closed off! Locking away other life forms like some kind of king! That's nobody's limitation but your own!
Yoko: That's right! We humans used to have someone much greater than us! For his sake alone... we'll keep on moving forward!
Nia: I've staked everything... on the greatness of the human spirit too!
Simon: Mark my words... this drill will open a hole in the universe! And that hole... will be a path for those behind us! The dreams of those who have fallen... The hopes of those who will follow... those two sets of dreams weave together into a double helix, drilling a path towards tomorrow! And that'sTENGEN TOPPA! And that'sGURREN LAGANN! My drill is the drill... THAT CREATES THE HEAVENS!!!
It's a slightly lesser example comparatively speaking, but no less epic...
Zafira: As long as we have life in our bodies, we will stand by each other.
Vita: We will always exist before our mistress, Queen of the Night Sky, Yagami Hayate.
Vita gets one all on her own in StrikerS, "I am the iron knight Vita, and this is the steel count Graf Eisen. There is nothing in this world we cannot destroy," which also gets turned back on her in the most heartrending scene in the series when she begins to despair thinking she cannot live up to it.
And then heartwarming when she does indeed live up to it.
Hayate, holding the bloody and near-dead Vita: The iron knight Vita and the steel count Graf Eisen. There is nothing in this world they cannot destroy.
"The Nanoha that you've always looked up to is an undefeated Ace who will not lose to anybody."
Cell: I admit. In terms of raw power you have me bested. My own strength doesn't even begin to compare. However, you still don't have a chance of defeating me. Not a chance in Hell.
Frieza has his fair share:
Frieza: I promise you, it will be a nightmare beyond the horrors of Hell!
Frieza: Oh, the look on your face, Vegeta. I'm guessing that means you really had no idea a being as powerful as me could exist after all! Now then. Which one of you should be the first to see Hell?
Frieza: I promised you, Didn't I? That I'd show you a nightmare beyond the horrors of Hell?
Frieza: Simian Bastard! I am Lord Frieza. None surpass me. No one even comes close! Etch this into your skull! I am the emperor of the universe! The likes of you are only fit to grovel at my feet! Or better still... to die! In disgrace! At the hands of your master!
Goku gets a heroic one earlier on, against Frieza.
Goku: You can destroy whole planets but you can never destroy what I am, friend!
Freiza: You... what are you?!
Goku: I am the hope of the universe! I am the answer to all living things that cry out for peace! I am protector of the innocent! I am the light in the darkness! I am Truth! Ally to good, nightmare to you!
The version in the redub Dragon Ball Kai is better (and also the first time Goku uses his full name in an English dub):
Frieza: You... You... WHAT ARE YOU?!
Goku: I'm a proud Saiyan who calls Earth home, and I'm here to defeat you. I am the warrior you've heard of in legend, pure of heart and awakened by fury, that's what I am. I AM THE SUPER SAIYAN, SON GOKU!
Goku: The killing stops here. All you can see is the light shining through the cracks around the edges of the door, Baby. And you just don't think that little bit of light can overcome your dark plans. But what you can't see is what's behind the door. That's what I am. ... Light breaks the darkness. This form is my instrument. I have no limits.
Baby: What ARE you?
Goku: I am the answer. The answer to all that is evil.
Vegeta has to be one of the kings of this trope. One of his best was when Babidi was controlling his body:
Babidi: Kill! Kill the Kai!
Vegeta: No! Get out of my head! I already told you! I will not be distracted from this anymore! I won't! It will take more than head games to stop me. You may have invaded my mind and my body...but there's one thing a Saiyan always keeps...HIS PRIDE!
Vegeta gives badass boasts like no man's business:
Vegeta to Kid Buu: What's so funny? FREAK! What are you gawking at? What did you think, huh? That I was going to roll over and die from an attack like that!? You're nothing, just a trickster... I am a warrior! The saiyan prince! VEEGGEETTAAAAAA!
Vegeta to (Semi-Perfect) Cell: Are you ready now? To witness a power not seen for thousands of years!?
Vegeta to Android 19: Silly Robot! Do you really think you have a chance against a Super Saiyan like me? Your brain must be malfunctioning!
While he ends up unable to deliver, Gotenks still gives a great one when he's introduced.
Gotenks: I understand. You're all scared, but Buu is nothing. I will bring him back, dead.
Vegetto, the potara fusion of Goku and Vegeta, even when turned into candy can still produce epic badass boasts.
Gohan gives an epic one to Cell during their battle in the Cell Games:
(Super Saiyan 2) Gohan to Cell: What are you so afraid of, Cell? Isn't this what you wanted? I warned you. I told you what would happen if you pushed me too far. But you didn't listen. You forced me to awaken my hidden power, and now that you've seen it, you're afraid... because you know that I'm going to destroy you.
(Metal) Cooler to (Super Saiyan) Goku: So the super saiyan has finally decided to show himself. Well I'd say it's only fitting, wouldn't you? You see this is the way I remember you best saiyan.... Hehehe. So this is how it should be when you die...
Gohan to Bojack: I know you kind; you think can just waltz in and take our planet. But you forget one thing... I'm my father's SON!!!
Broly to Goku: You Kakarot. I choose you to be the first of my victims.
Goku to Broly:Your final hour has arrived!
Gogeta to Janemba: I am neither Goku or Vegeta, I am Gogeta! It's over Janemba, I've come for you!
(Super Saiyan Three) Goku to Hirudegarn: Fight me...if you're ready to die.
Beerus: Is there nobody on Earth more worthy to destroy…?
Subverted when Vagabond's Yoshioka Denshichirou tries to use his lineage (he's the son of famous samurai and Master Swordsman Yoshioka Kempo) against the intimidating and highly-skilled Sasaki Kojirou, only for Kojirou's companion Ito Ittousai to point out that not only does Kojirou probably not know who Kempo is... but Kojirou's deaf and doesn't even know what's being said. (Later on against Miyamoto Musashi, Denshichirou admits that this was nothing more than an attempt to intimidate others when he was scared himself.) Used much more effectively by Musashi later, who otherwise usually avoided this:
Lelouch: I am Zero. The man who leads the Black Knights, who challenges the Holy Britannian Empire. The one who holds the entire world in his hand.
And let's not forget:
Lelouch: My name is Lelouch vi Brittania, eldest son of Empress Marianne, the prince who was abandoned by his empire. If anyone wishes to stop me, let them try. If there is anyone who can go beyond my despair.
Lelouch: We have nothing to fear. My name ... is the future of this world!
Lord Jeremiah Gottwald (a.k.a. "Orange boy") gets one as well when fighting Anya:
Jeremiah: Memorize this! Memorize Jeremiah Gottwald! Commit it to memory, because that's the memorable name of the man who has defeated you.
Lelouch is full of these. For another one, right after he regains his memories in the first episode of R2:
Lelouch: The world has to change, and I will change it.
Urabe: We've been waiting for you, Master Zero. Please, give us your orders.
Lelouch: Very well, because after all, I am Zero! The one who will crush the world, and the one who will recreate it anew!
From the Black Knights' public debut:
Lelouch: Wherever oppressors abuse their power by attacking those who are powerless, we shall appear again, no matter how mighty, how formidable our foe may be. Those of you with power: fear us! Those of you without it: rally behind us! We, the Black Knights, shall be the ones who stand in judgement of this world!
And when Zero makes his big return in Season 2:
Lelouch: So long as the strong oppress the weak, my rebellion will continue to grow! It begins today with the divine punishment I have wrought upon the inept and foolish Viceroy Carales. I shall fight, against all those who abuse their power!
And in the final episode:
Lelouch: Attention entire world! Hear my proclamation: I am Lelouch vi Brittania, Emperor of the Holy Brittanian Empire and your only ruler. Schneizel has surrendered to me. As a result of this, I am now in control of both the Damocles and the FLEIJA weapons, and even the Black Knights no longer possess the strength to oppose me now. If anyone dares to resist my supreme authority, they shall know the devastating power of the FLEIJ As. Those who could challenge my military rule no longer exist. Yes, from this day, from this moment forward, the world belongs to me!
Lelouch vi Brittania commands you: Obey me subjects! Obey me world!
In Naruto the title character gets quite a few, but one in particular stands out:
Naruto: It doesn't matter how strong my opponent is. If he tears off my arms, I'll just kick him dead. If he tears off my legs, I'll bite him dead. If he tears off my head, I'll stare him dead. If he gouges out my eyes, then I'll curse him dead! Even if I get chopped into pieces, I'm gonna beat Orochimaru and take my friend, Sasuke, back once and for all!
And Shikamaru of all people proves to be pretty badass, when he's willing to get OFF his ass.
Shikamaru: You and your god don't frighten me. You see, you and I believe in different things. You wanna know what I believe in? The Will of Fire. Right now, the god you should be worried about isn't your stupid Jashin or anyone else; it's me... because I'm the one who's about to pass judgement.
Though Itachi Uchiha is usually a person of few words, he knows how to wax intimidating.
Itachi: Every Jutsu has a weakness. And that jutsu'snote Impure World Resurrection weakness... is me.
Sakura Haruno does not take Sasori namedropping Orochimaru very well.
Sakura: I will get you, do you hear me?! You can blow my limbs off. You can poison me 'till I can't move any more, but I'm still going to get you! No matter what you pull, no matter what you throw at me, I'm going to make sure you tell me everything about Orochimaru! Is that clear?!
Madara Uchiha to the Five Kage after destroying a mountain:
Madara: Too bad [Hashirama's] not here. Though in a way, it's a good thing for all of you. If it's just me... they won't have to redraw the maps too much.
Hachi: In Soul Society, there are no Gods other than the Shinigami — the Gods of Death. So perhaps we cannot fully understand the weight of your words... Forgive us for our unbelief, "God" of Hueco Mundo.
Aizen: Observe... I am perfectly capable of reaching your heart at any moment.
Yamamoto: There hasn't been a shinigami stronger than me born in the last thousand years.
After an enemy comments on the lack of security at 1st Division Headquarters:
Yamamoto: I am here. There is no better security than this.
At the end of chapter 505:
Yamamoto: "It has been over 1000 years, Juha Bach. I have come here TO ANNIHILATE YOU."
And at the end of the next chapter:
Yamamoto: I was waiting, indeed. So that I can smash your flesh, blood, sword and soul into many tiny pieces. Bankai. Zanka no Tachi.
Particularly of note is the number two Espada, Barragan Luisenbarn. Virtually every word out of his mouth is one of these.
Barragan: You're trying to figure out my power, but can't, aren't you? Each Espada represents an aspect of Death. These are ten reasons why people die. Loneliness. Sacrifice. Nihilism. Despair. Destruction. Intoxication. Madness. Rage. And my aspect is Old Age. 'Old Age', meaning 'Time'. It is the most powerful, and most inevitable aspect of Death. Everyone must face it eventually. Look...with just a touch, I can rot your very bones.
Barragan: Of course you can't comprehend it. That's just the way Death is. And from now until the end of this battle, there will not be a single thing you can understand. Rot, Arrogante.
Barragan: Did you think that Kidou does not age? How amusing. People die, animals die, and even Shinigami die eventually. Old age is a fate suffered by everything that can die. If the things built by humans can rot and die, then so too can the Kidou that Shinigami create. There may be Kidou that can last over a thousand years, but there can be no Kidou that last forever.
Barragan: Hollowfication? Clever! But who do you think you're playing Hollow at!? I am the Great Emperor, Barragan Luisenbarn! The God of Hueco Mundo!
Barragan: Puny! Miniscule! Worthless! Shinigami, Hollows, Arrancar, and the animosity between them...quarrels, will, freedom, beasts, plants, the moon, the stars, and the sun, all these things are beneath my notice. Only my power is absolute. All other things are equal in their insignificance. I possess the ultimate power. The world shall be under my rule! There can be no equality between us. behold: in my cavernous eyes, your lives are no different from an ant's.
Barragan: With these hands, I will make sure to kill you. You will regret giving me power. I am King! I am God! I will never die! And I will target you for all eternity, Sōsuke Aizen!
As you can see, whether he comes off as badass or a boring ball of Narm depends largely on the quality of the translation.
Kenpachi Zaraki is a gold mine of such boasts:
Kenpachi: I'll let you go ahead and have the first strike. I'll stand here and you can cut me any way you want. You can go for my throat, or my gut. Take out my eyeball if you want. Or, if you're lucky you might kill me with a single strike.
Kenpachi: I only wear the bells and this eyepatch to make things harder, so I get more enjoyment out of my battles. I'm glad you're taking advantage of them, because otherwise, they don't serve any purpose.
Kenpachi: When I fight, I make sure to hold back. I never swing my sword with my full strength. Do you see why? If I didn't, my enemies are so weak, the battle wouldn't last long enough for me to enjoy it.
Kenpachi: Sanity? I've never had such a useless thing!
Kenpachi: A fight to the death huh? That means I can come at you with everything I got and then after you're dead, go reincarnate yourself so I can kill you all over again.
Kenpachi:What's that face for? Did you imagine that I couldn't cut you? I'll only say this once, with your imagination, there's not a thing you can create that I cannot cut through. Because I am the "Kenpachi".
Neliel, right before taking on Nnoitra and right after Nnoitra handed Ichigo his ass:
Neliel: Don't worry. This won't take long.
Light Yagami in Death Note: "I will be the god of the new world!" and, "I AM JUSTICE!"
Hibari Kyouya of Katekyo Hitman Reborn! is nigh-unstoppable, and has a couple hundred of these. The best are his catchphrase "I'll bite you to death" and when he tells an enemy that his Vongola Ring, which works via the wielder's determination, worked on how royally pissed off he was. He is more or less always angry, but that enemy ended up making it a LOT worse.
Black Star from Soul Eater occasionally messes up, but normally proceeds to kick ass after telling his opponents how he is "the man who will surpass God".
Black Star:Holy am I alone throughout heaven and Earth! I am the star! Got that!?
Professor Stein getting involved in any conflict is pure badassery in the first place, but his catchphrase take it up to eleven. "I will dissect you."
Seto Kaiba ends just about every sentence with "Now if you'll excuse me, I have a multi-million dollar company to run!" He then proceeds to swagger off, leaving all the other characters rather confused and angry.
Yami Bakura "You poor fool. Don't you realise that I am the darkness?"
Hajime No Ippo: Takamura does one to Bryan Hawk, although in his head.
"That smug look of yours... I bet you've never lost a brawl before, have you? Unfortunately for you... That's only because I've never been to America!"
He also does one in a match against a random opponent that managed to really piss him off.
"Smirking like that... pissing me off! And what are you looking so happy about? That pisses me off! That really pisses me off! All you people are PISSING ME OFF!! Who do you think I am? I... AM... TAKAMURA MAMORU-SAMA!"
Ippo, himself, gives a pretty badass boast before a title defense match that directly proceeds Takamura's own title defense match. What makes it so badass is that Ippo always sees himself as the underdog who has to struggle to win. He's just filled with so much rage at his opponent for talking down about his friends and mentor that he's snapped.
"This won't take long."
Final Fantasy VII: Advent Children features duelling boasts, delivered by duelling enemies. At the conclusion of his fight with Sephiroth, Cloud tells him, "Stay where you belong. In my memories." Sephiroth's response to this is to look Cloud in the eye and declare "I will...never be a memory."
From Zombie Powder, we have Gifful, the Great Undead Box. "There is nothing that can kill me! You still think I am a small fry? Huh, Akutabi Gamma?" and the response...
From Gintama: "Listen, I don’t care what you guys do around the universe. This is my sword, and anywhere it can reach is my country! Bastards who come in and try to mess with my things... whether it be a general, whether it be space pirates, whether it be a meteorite... I’ll destroy them!"
Natsu: "Mages of Fairy Tail specialize in property damage!"
Natsu: "I’m gonna stop it! Even if it splinters my body, I’ll just stop it with my soul!"
Gray: "Sorry, but it doesn't matter if you're a woman or even a child. I don't go easy on anybody who hurts my comrades."
Lucy: "Spirits aren't shields! I fight alongside them! That's my style!"
Erza: "My companions make my heart strong. If I'm fighting for those I love, I care not what happens to this body."
Gajeel: "I don’t even know the meaning of going easy on someone."
Makarov: "You have laid hand on the monster's children. Don't think any human laws will protect you."
Laxus: "I came to visit Mavis's grave, and looky what I found? The Second Master's here, too. Since you're here and all, maybe I'll make a grave for you, too!"
Laxus: "That power was just from one leg. I've got another one. And both my arms. I have my head, and my entire body. If I attack with all of them at once, we're not talking two or three times stronger... Wanna try me?"
One of the most unnerving ones in the entire series is answered with what is arguably an even more disturbing Badass Boast, simply because of whom it is coming from, and the look in her eyes as she says it.
Zeref: "It will be a one-sided massacre. Not a single soul will be spared my wrath."
Gates: You little shit! Just who in the hell do you think you are?!
Sousuke: Who, me? I'll tell you exactly who I am. (powers up Lambda Driver) I really couldn't care less about Mithril... (slowly starts walking towards Gates) I'm Class 2-4 at Jindai Tokyo Municipal High School.
Gates:(uneasy) Hey now, I've still got a hostage here!
Sousuke: I'm student no. 41. (energy field starts forming around his fist) I'm in charge of waste disposal and umbrellas.
Ookiku Furikabutte: Tajima says in episode 2 that, "I can hit any ball. I've never seen a pitch I couldn't hit by the end of the game." As of 2012 this hit streak is still intact.
In Getter Robo Armageddon, Ryouma catches the Metal Beast Getter G in mid-combination. As Saotome struggles, Ryouma tells him, "C'mon, doc! Can't even pull off a Change without looking at the controls?!", Hayato adding "Looks like that's something you learn from a real team!"
Stanford: Are you afraid?! There's no way you're not! Now witness the awesome power of— *BANG* Revy: Shut the fuck up.
Eda's retort to Chang in chapter 56:
"And another thing, smack talk has no effect on those stronger than you. You and your men have the power to bring men and whole companies to your heels, but we have the power to bring entire nations to our heels, if not to ruin."
"Fools! Your Pokémon attacks cannot weaken me. My powers are too great. No Trainer can conquer me."
Pokémon Origins, an OVA retelling of the first games, begins its final episode with one from the rival, Blue.
"I've always been one step ahead of you from the very beginning. While I was working on my Pokedex, I searched everywhere for the perfect Pokemon! I specifically looked for those teams that could beat any Pokemon type! Now, I stand right here at the top of the Pokemon League! Do you know what that means, Red? ... I'll tell you! It means that I am the most powerful Trainer...in the world!"
Levi claimed that he alone could put Titan!Eren down like a dog if needed. Going by the fact he wrecked the Female Titan, who had easily killed highly experienced soldiers, this was no bluff.
Mikasa gives a chilling one during a standoff with soldiers who were about to execute Eren
Mikasa: My specialty... involves flesh... and the lacerating thereof. You just draw close enough, and I'll be happy to demonstrate. Should anyone wish to experience my technique... by all means, feel free to come this way.
Kirito of Sword Art Online gives a spectacular one to Sugou after disarming him in the real world.
Kirito: *Examining the kabar* This weapon is pitiful. It's too light... has no reach. Guess what. It's more than I'll need to kill you.