Names to Run Away From Really Fast: Quite a lot of pirates and Marines, actually. Arlong (actually given the translation Er-Long/惡龍 IE. "Evil Dragon" in the Taiwanese Versions), Don Krieg (krieg being German for war), Das Bones (Mr. 1's real name), Bartholomew Kuma ("kuma" being Japanese for bear, and not the Caring kind), Fleet Admiral Sengoku ("sengoku" means "warring states" and was a feudal period of Japan's history), Admiral Akainu ("akainu" translates as "red dog"), Marshall D. Teach (Teach being the real Blackbeard's assumed surname), Dracule Mihawk, Crocodile, Capone Bege, Captain Kidd, and, oh, who are we forgetting... KILLER.
Some of the protagonists have fear-inspiring names: Try Roronoa Zoro, for instance (the surname of a cunning pirate, and the forename of you know who).
Most notably Magellan of Impel Down. The very idea of fighting Magellan is considered suicide by nearly everyone, those that try to fight him are usually overconfident, ignorant of his strength, or Too Dumb to Live. This trope is further invoked when Magellan upgrades to an Advancing Wall of Doom, and the only option anyone has at that point is to run away really fast.
Impel Down's Captain of the Guard Sadie-chan, who takes her name from the word "Sadism".
Inverted in a couple of cases. "Chopper" sounds scary, until you meet him and realize he's a cute li'l reindeer with self-esteem issues. A guy named Doflamingo sounds as threatening as potatoes, but he's actually one of the most deranged and frightening characters in the manga.
Necromantic: One of the reasons that Dr. Hogback got into the profession of sticking shadows into corpses.
Nepotism: Heavily implied (if not outright stated) to be the reason why Spandam is the Chief of CP9, despite being a General Failure and an all around waste of human life. His father, Spandine, was also Chief of CP9, and was decidedly more competent and had standards (unlike his son), though he was almost as much of a Jerkass.
Never Mess with Granny: Doctor Kureha. One hundred and forty years old and will kick your ass if you so much as look at her funny.
Never Say "Die": Given that it was 4Kids that did the initial English dub, it comes as no surprise that the anime was a victim of this. It got to dark energy disk-levels of absurdities (as well as shoddy editing) with Nami's flashback.
Never Say That Again: Robin tells Franky to never make a face or speak again while he's inside Chopper's body.
Never Smile at a Crocodile: Obviously Sir Crocodile. It also applies to the Bananadiles (huge crocodiles with a small banana-shaped thing on their head) and to the rivers of Luffy's homeisland. The 10th film offers the "Land Gator", a huge, flat crocodile living on Merveille.
New Powers as the Plot Demands: An epedemic in the Enies Lobby arc. Each of the Straw Hats, save for Robin (who doesn't get any major battles due to being captive for most of the arc) and Franky (since this arc is his debut as a fighter) displays a new attack, form, or weapon.
Zoro gives this trope something of a lampshading during his fight with Mr. 1. When he learns that Mr. 1's power grants him a steel body, Zoro thanks him. His reasoning? When the battle ends, Zoro will have learned how to cut through steel.
With the new timeskip, Chopper's got a new Nice Hat and Usopp has one too.
What, no love for the Soul King's crown?
In chapter 603, Rayleigh's flashback hints that Luffy's hat, given to him by Shanks, was once the property of Gold Roger.
Hello? Law's got a pretty sweet hat, and looks more like the style of Chopper's after the timeskip.
Nice Job Breaking It, Herod!: The government's attempts to find Roger's unborn baby. They were never able to find the child, because the mother deliberately stayed pregnant for twenty months through sheer force of will in order to protect her child. That child would later grow up to be one of strongest pirates in the world: Portgas D. Ace, Commander of the Second Division of the Whitebeard Pirates, and the older adoptive brother of Monkey D. Luffy.
Nice Job Breaking It Marines: The World Government tries to put Gold Roger to death so they can discourage piracy. Roger screws it up by inspiring the Golden Age of Piracy with his words about One Piece. Apparently having failed to learn from this mistake, they try it again with Ace, knowing that Whitebeard will surely try to prevent it. Killing both would send a much bigger warning. While they succeed in killing both, Whitebeard does as Roger did and confirms the existence of One Piece, ruining the entire plan. Then, Blackbeard shows up and steals Whitebeard's earthquake powers, putting the power to destroy the world in the hands of someone who would actually do it. See Villain Ball below for more details.
Immediately afterward, we find that Jinbei wasn't just blowing smoke when he said that several islands were safe only because of Whitebeard. After word of Whitebeard's death gets out, we find that several islands on the Grand Line and in the New World have instantly become hellholes now that the nearby pirates realize they can do whatever they want without fear of a reprisal from Whitebeard. Nice one, Marines; if you were trying to create peace, you just took a HUGE step backward from that.
To add icing to their failure cake, the Marines have run themselves ragged with their war on Whitebeard, and now lack the resources and people to properly protect all of the islands that they could previously protect. Oh, and now they also have a much stronger pirate to worry about who just couldn't care less about the balance that Whitebeard had provided. Epic Fail doesn't even begin to describe the consequences of their actions.
Turns out that Trafalgar Law and the Straw Hat Pirates' actions in Punk Hazard are the direct cause of current events in Dressrosa, as Doflamingo's pretending to follow their demands to abdicate his role of Warlord and as king of Dressrosa was such a blow to Dressrosa's rebels that it pushed them past the Despair Event Horizon and resolved them to go out in a blaze of glory Suicide Attack. Even Robin displays a horrified Face Fault right alongside Usopp and Franky when they realize this.
Nice Job Fixing It, Villain: To get rid of Luffy, Eneru traps the pirate's arm inside a huge ball of gold. Guess what Luffy uses to stop Eneru's Final Smash?
Caesar Clown tries to get back at Smoker by crushing his heart. It ends up being his subordinate Monet's heart, stopping her just before she pulls the lever to release poison gas.
Nightmare Fetishist: Perona, who thought her animal zombies were the cutest things ever. Also Robin, who declared Thriller Bark's zombie cerberus "cute."
Many others also qualify, but these three count on a more literal level. Franky and Kuma are both Robot Pirates and Brook is a zombie pirate with a touch of ninja thrown in.
Being a series about pirates, almost everyone fits this trope, with some hitting multiple levels. You have a pirate thief navigator, pirate fish kungfu, pirate robot gangster shipwright, pirate reindeer doctor, pirate pervert chef, princess bountyhunter...
Nobody Poops: Averted. Luffy has asked Brooke and Caimie if they poop. Also, it seems that there are toilets on the Sunny. It's probable that people do poop, we just never see it.
Inverted HARD with Warden Magellan, who spends 10 hours per day suffering from the diarrhea caused by his love of eating horribly poisonous food (which he is immune to dying from thanks to his Devil Fruit making him a Poison Man). With eight hours of sleep, this leaves him only four hours to do his job.
No Celebrities Were Harmed: It's a recurring gag. Notable examples include Jango (Michael Jackson), the Admirals Aokiji, Kizaru, and Akainu (based on Yusaku Matsuda, Kunie Tanaka, and Bunta Sugawara respectively), and Franky (Jim Carrey)'s Ace Ventura.
Several of the pirates share the names and/or are based off of real life pirates. The most obvious being Blackbeard, but Captain Kidd and Bellamy as well.
No, Except Yes: King Neptune is uncertain whether he should have the Straw Hats arrested for a crime they were predicted to do. He then tries to capture them anyway so he has time to mull it over.
No Export for You: One of the more teeth grindingly annoying instances of the UK getting absolutely shafted by Toei. Manga, bless them, keep trying; Toei is just plain stupid and price it far too high.
Long since averted. The first 3 movies and Strong World have also been released.
Tilestone of Galley-La in the original. It gets so bad that his coworkers force him to stand several feet away just to carry on a normal conversation.
No-Holds-Barred Beatdown: Crocodile thoroughly trounces Luffy and leaves him for dead in their first encounter, and Aokiji does something similar later on. The fight, if it can be called that, against Kuma is a slightly less malevolent example, since although the Straw Hats can do absolutely nothing to him, the crew is effortlessly defeated and scattered across the seas rather than being killed.
Then there's Luffy's fight against Magellan, the warden of Impel Down, whose poison powers force Luffy to get treatment that takes off ten years of his life. Though that one may be more of an epic No Sell.
Oars Jr. vs. three of the Seven Warlords of the Sea. It can't even be called a fight. Oars Jr. takes the full brunt of Kuma's Ursus Shock attack, gets his leg sliced off by Doflamingo's Razor Floss, and finally gets freaking impaled by Gekko Moriah's shadow spear.
"No. Just... No" Reaction: Robin to Franky. As a human being, it is too embarrassing to mention how many times she forbids him from docking or making facial expressions or speaking ever again ( last two when he’s in Chopper’s body).
Non-Nazi Swastika: A swastika was incorporated in the crest of the Whitebeard pirates. This was changed in the anime to crossbones in a + shape. The manga later Retconned the symbol to match.
Non-Serial Movie: There are currently ten movies produced by Toei Animation. While most of them can fit into the anime's continuity fairly well, there are a few, such as 3 and 9, that cannot.
The tenth, Strong World, was actually written by Oda, and so was mentioned In-Universe Manga and a few anime episodes were a prequel to the movie.
Noodle People: A number of characters are somewhat lanky, but this trope reaches its zenith with the women, who are very often frighteningly rail thin. They have gotten a little bit better due to recent Art Evolution, though.
Some characters are of average breadth... offset by a ridiculous height. The Admirals are a perfect example of this.
In many ways, Bartholomew Kuma firing a massive air-compressed bomb which the resulting explosion covered all of Thriller Bark was a massive case of this, as not only did everyone present survive, but Zoro got up to attack him, followed by Sanji on his feet as well.
Only mildly subverted that Kuma was aware that they survived his attack. Just not so much when he allowed Zoro to take in Luffy's pain.
More recently after a short fight with Magellan, Luffy was so badly poisoned that his death was all but guaranteed. Even when Emporio Ivankov healed him all it did was raise his survival chances to 2 or 3%.
Subverted again with Whitebeard getting ganged up on by Blackbeard's entire crew after losing half his head to the same Admiral that killed Ace, and dying. Granted, the losing half his head thing could be playing it straight.
Technically, the description of the wounds from the Marineford arc Whitebeard took at the time of his death are worth noting for this. Whitebeard had taken 267 slashes/stab wounds, 152 gunshot wounds, and 46 wounds from cannon balls, not counting the damage done by the Marine Admirals. All this while having been shown to have failing health for most of his previous appearances.
No OSHA Compliance: Quite a few of the World Government's facilities where large numbers of soldiers or personnel are expected to be present. Enies Lobby, for example, is situated above a massive void to the center of the planet and yet there's no safety rails at all. Impel Down also counts, as some of the hellish environments the prisoners are forced to suffer in affect the guards as well (they don't seem to be to fond of being sent down to patrol the 100+ degree heat of level four...).
Nosebleed: Deconstructed. Sanji, having not seen a woman for two years spontaneously has nosebleeds when he sees one, causing massive bloodloss and in need of a blood transfusion. Of course, he has a rare blood type and the Straw Hats are on Fishman Island, where it's illegal to mix blood between humans and fishmen.
No Sense of Direction: Both Luffy and Zoro, although Zoro is much, much worse. Seriously, how does he do it?! In the G8 filler arc, he managed to get lost in a straight corridor.
What, you think that is bad? Zoro gets lost in a straight line —a dead end— on the "Red Light, Green Light" ("Darumasan ga Koronda") filler game in the Long Ring Long Land arc! He looks astonished saying the path is gone... cue Sanji criticising Zoro's poor sense of direction from the obviously correct pathway.
No Swastikas: The flag of the Whitebeard Pirates, as well as Ace's back tattoo, while originally sporting manji (very similar to swastikas) are changed to vertically-aligned crossbones in the anime. The manga later followed suit after the author's editors told him the symbol was now off limits. In neither case does this diminish even slightly the sheer badass of either Ace or Whitebeard, making you wonder why Oda felt he needed it in the first place.
Later editions of the VIZ manga keep the mark with a short editor's note explaining that manji is NOT the same thing as a swastika.
Not Blood Siblings: While it was a common fan theory that Ace and Luffy weren't related, the real shocker was who Ace's real father was. Although, it makes it all the odder that Ace does look somewhat like Luffy and shares a lot of the Monkey family's quirks.
They all share the mysterious D initial, so maybe they are more distantly related.
Not in Front of the Kid: Queen Otohime stops the fishmen from releasing years upon years of pent up anger and oppression in a brutal massacre with one simple phrase: "The children are watching."
It gets rather unnerving following recent events when looking back on Luffy and Teach's initial meeting and seeing how similar they were. He even complimented and encouraged Luffy.
During the Marineford War, Doflamingo mentions to Crocodile that they aren't that different. It's revealed in the Dressrosa Arc that Doflamingo destroyed a current-standing monarchy and took it over years before Crocodile went after Alabasta.
Not-So-Harmless Villain: Recurring villain Buggy the Clown and crew's recent appearances are beginning to suggest that they might mean business after all. It has also been said by Oda Buggy has the potential to be at Shanks' level, he just didn't train or face tough enough foes to gain experience.
Gin of Don Krieg's crew, who was so shell-shocked from his encounter with Mihawk and nearly starving to death that it would have been difficult to peg him as Krieg's actually pretty damn tough right-hand guy before The Reveal.
No True Scotsman: Jimbei and many other Fishmen rightfully consider Arlong a disgrace to their species by letting monstorous racism toward Fishmen turn him into a monstorous racist toward humans.
Not Quite Saved Enough: Luffy has spent the last year searching for Ace, going from the bowels of Impel Down Prison to Marineford, fighting insanely strong enemies, making unusual alliances, enduring his allies' heroic sacrifices, and literally gambling his life away so he can get to Ace, and just as he's been freed he's killed by a stronger fighter. At least Ace gets to say his last words.
Not Rare Over There: The Straw Hat Pirates decide to act like pirates for once and make off with a bunch of gold from the Skypieans... but it turns out that gold is extremely common there and they'd be happy to just give it away.
Now You Tell Me: Pretty much the entire crew at Vivi when they go traveling through the lands of Alabasta and get caught up by all of its various dangers and traps.
Obligatory Swearing: Perhaps in an effort to distance itself from 4Kids and the general perception of One Piece being overly kiddy, the uncut Funimation dub is one of the more foulmouthed dubs heard. Though the strongest they ever go is "shit" (courtesy of Buggy and Sanji), it is a bit jarring to count up a total of thirty swears in one particular episode.
Chopper has a similar tendency, though only when he's being complimented, showcasing his insecurity and dislike of humans by dancing in joy while insulting them.
Obviously Evil: Gekko Moriah, Spandam, the newer additions to Blackbeard's crew, Blackbeard himself, ALL Level Six inmates, Wapol, the Celestial Dragons, Captain Morgan, Donquixote Doflamingo.
Perhaps subverted in Moria's case with the revelation that he was just like Luffy at one point, since he had good True Companions who were all wiped out by Kaidou, with him barely surviving. Imagine, Moria like Luffy!?
Occam's Razor: Played with. The Straw Hats receive a distress call that mentions how cold it is, but the island it came from is boiling hot. While Usopp puzzles over this, Luffy suggests the caller was just an idiot.
Ocean Punk: It's not called "The Great Age of Piracy" for nothing.
Oddly Common Rarity: Devil Fruits. In the East Blue Arc, they were rare. In the Grand Line, it's much more common for pirates to have them. Four of the nine members of the Straw Hat crew (including Luffy himself) have Devil Fruit powers.
Remember, Devil Fruits were only stated to be rare while the story was still happening in the East Blue, and Don Krieg specifically stated that they were far more common on the Grand Line, going so far as to note that finding ways to effectively take on Devil Fruit users would be essential if he was to get anywhere on the Grand Line.
the fruits itself are rare with them being seen a grand total of 6 times, 2 of those during a flashback
The Seven Warlords of the Sea have Blackbeard, who doesn't have an animal theme.
The Blackbeard Pirates begin with Doc Q, who is not named after a historical pirate like the rest (although they later pick up Shiliew, who is also not included in this naming theme).
Of the Eleven Supernovas (including Zoro), only Luffy and Killer are not named after historical pirates.
The three ancient weapons are named Pluton, Poseidon, and Uranus. They're all classical gods, but the fact that Hades/Pluto and Poseidon/Neptune are two members of the "big three" Olympian gods led many to believe that the third weapon would be named after the third member of the trio, Zeus/Jupiter, as opposed to Uranus, one of the primordial gods.
Offstage Villainy: Eustass Kid. The only rookie with a bounty higher than Luffy's before the timeskip. Reason being is his violent behaviour (read: killing anyone who laughed at him), yet we don't really see it ever happen. Until chapter 594, that is.
In general, any pirates that aren't explicitly antagonists will usually have only verbal indication of how they got their bounty, if that.
Oh, Crap: Rob Lucci who remained calm and determined during the extremely long and grueling fight with Luffy, finally was shocked to the core in the last seconds of the fight when Luffy refused to fall down even after taking his ultimate attack (much weaker version of which disabled Luffy for a time just a few minutes earlier) straight to the chest.
This is Eneru's reaction on realizing his lightning-based Devil Fruit powers have no effect on Luffy, whose own fruit power has made his body into rubber (with rubber being a good insulator for electricity).
Arlong has a minor one when he removes Zoro's bandages in episode 41 and wonders how he's still standing.
The usually-stoic Zoro gives one when he realizes that Pica's plan when fighting him was to lure him far away from Usopp, Riku and the others so he couldn't save them in time. Zoro gets over it quickly enough, though.
One-Man Army: Capone "Gang" Bege, one of the Supernovas, is literally this. His Devil Fruit power allows him to store miniaturized soldiers and supplies inside his body, releasing them (and transforming them back into full size) to do battle. This basically makes him a human-sized walking fortress.
Who are we kidding? The whole series is filled with One Man Armies.
One Super One Powerset: Devil's Fruit abilities are stated to never get stronger per se, but you can discover new and better ways to use them. It is also a rule that you can only use one, that you'll die if you try to gain a second, but Blackbeard seems to have found a way around that.
Only a Flesh Wound: Massive amounts of blood loss keeping Roronoa Zoro down? Nope, he's good! Subverted when he initially seems to be recovering just fine from his battle with Kuma, only for his injuries to bite him in the ass much later.
Only I Can Defeat Him: Usually, Luffy is the only who can defeat the strongest antagonist of each arc while the rest of the Straw Hats deal with his subordinates.
Subverted in the Fishman Island Arc. The Big Bad of that arc was defeated by Zoro with one slash, and it became increasingly clear that any one of the Monster Trio could have defeated him. The fact that he was the strongest and the leader of the antagonists, no matter how weak he was compared to them, is the only reason why Luffy bothered to fight him at all.
Only Mostly Dead: Luffy, after getting covered in poison and thrown into level five of Impel Down.
Zoro, after his fight with Mihawk, then Hatchan, then much later, Mr. 1
The Only One Allowed to Defeat You: Zoro has this mindset against Mihawk. And, to a more obsessive extent, Gold Lion Shiki feels this way towards Roger. So much so that he spends 20 years working on a plan to eradicate the "new age" that he feels is an insult to the age he and Roger lived in.
Robin is an interesting case, as while she is The Stoic (and, on the surface, the only vaguely sane crewmember), she also blithely accepts all of the crew's weirdness with a motherly chuckle while providing her own morbid brand of weirdness. She appears to be the only sane one, but doesn't really take the role of Only Sane Man.
In Buggy's Impel Down crew, Mr. 3 is the only one that can see Buggy isn't all-powerful.
As other pirates see it, the world is this to the Straw Hat pirates. No ordinary pirate would dare even disrespect the World Nobles. The Straw Hats not only have no idea who those people even are at first, but both Zoro and Luffy attack them (Zoro was stopped, Luffy succeeded). The reactions of the other pirates range from impressed to angry.
As of Chapter 579, Coby.
Smoker and Tashigi realized what the Marines were doing was wrong as well; Coby was just the first to say anything about it.
Only Six Faces: Averted. While in the earlier years there were some characters that looked familiar, particularly the women, now a days every single character has a very distinctive look. Even one shot characters that die the chapter they're introduced or random people littering the background. The only time characters look the same is when it's done deliberately due the the characters being related or being used to draw parallels between a character and another character with a similar world view from a previous generation. Of course, given the sheer size of the setting, this involves a lot of gonk going around...
Played straight with post-time skip Robin and Boa Hancock, because they look exactly the same in close-ups. They're not even related. Some readers even wonder why Robin is in two distant places at the same time...
When part of Baroque Works, the first time Robin (as Miss All-Sunday) showed up on the Going Merry, Sanji held her up with a pistol. It's the only time he's ever threatened a woman in the entire series. Usopp even hung a lampshade on it.
When Luffy order his crew to run away from Kizaru. For an Idiot Hero who has always fought against the enemy, no matter how bad the odds were, this was pretty significant.
Also, after Ace dies. For the first time, Luffy has doubt in his dream of becoming Pirate King and thinks of himself as weak.
Nami actually giving away treasure to Lola. This is Played for Laughs as both Luffy and Ussop freak out when they witness this moment and think it's a sign that a storm's coming.
Ooh, Me Accent's Slipping: In the 4Kids dub, not only were the accents themselves both out of place and laughably fake (you'd think they'd never even ventured outside of Manhattan, judging by the Sanji's pathetic "Joisey" schtick), but they also had a tendency to stray quite a bit from whatever it was they were attempting.
The "best" example is probably Shanks, whose dubbed accent wandered all over the place, but seemed most like a bad impression of Bert the Chimney Sweep... though it's pretty much impossible to tell what they were after, really.
Ordered Apology: Inverted, Zoro demands Luffy to wait until Usopp apologizes Luffy of his own volition. It can also be seen as a double subversion, because Usopp's apology happened only because Zoro was so adamant about it in the first place.
Organic Technology: The Den Den Mushi. There's an explanation on how they work in the SBS, but that just drives it home further. Of course, given the ridiculous nature of the series and SBS, they fit right in.
Our Dragons Are Different: A filler arc introduces the Thousand Years Dragons, a race of pacific, fur-covered dragons, and Ryuuma was said to have slain a flying dragon in the past.
On Punk Hazard, an island half wreathed in flames and half freezing cold, there's a giant dragon. It breaths fire and also has Adaptive Ability to weather environments. There's another one in the other half that's covered in snow and ice that's smaller, faster and stronger than the other one. Both of them are artificial creatures, created by Dr. Vegapunk.
Moreover, in contrast to the Sennenryu, which are eastern type dragons, the one on Punk Hazard is clearly western types. And they're actually canon.
And now we're introduced to another dragon, implied so far to be Kinemon's transformed son. This dragon can talk, and looks clearly Chinese.
In the SBS for volume 63 Oda explains that it's only the merMAIDS that split.
Our Werebeasts Are Different: Zoan fruits turn the recipients into werebeasts. They tend to be dangerous mass of muscle even if the template creature was relatively harmless (this is also a general tendency among werebeasts. A werehamster can be as dangerous as a werewolf.)
Our Zombies Are Different: Type V and C. Shadow-Shadow Fruit allows Warlord of the Sea Gecko Moria to steal shadows off living people, and then put them in corpses reconstructed by Dr. Hogback via surgery. These zombies retain the personality traits and fighting abilities of the original owner of the shadow.
Out of Body Experience: In a recent chapter, we discover that Brooke can have his soul leave his body. This might just be the thing that will help get him, Zoro and Usopp out of the situation that they're currently in.
Out of Focus: The Straw Hats were literally pushed out of the story so that the focus could be shifted to Ace and the Whitebeard Pirates, only making cameos on the chapter covers.
Outside-the-Box Tactic: A Devil Fruit power sometimes provides an unforeseen advantage against another power. One of the more prominent examples would be low-tier villain Mr. 3, whose power to create objects out of wax ends up temporarily providing the single best countermeasure against poisonous Implacable Man Magellan.
Another one is Princess Shirahoshi's father King Neptune who locked up his daughter for ten years to protect her. However, it is justified as a Stalker with a Crush was sending her "love letters" in the form of swords and axes that could track her like a missile and are only stopped when they hit something.
Usopp is one of the weakest members of the Straw Hats. He cannot do half the things the strongest can do. Note that this doesn't mean he is weak, just weak to people like Luffy, Zoro, and Sanji. He will take your ass down if need be.
New World Pirate Cavendish entered the New World with a bounty of 220 million three years ago and was all the rage and fear in the papers. Then came the Whitebeard's Summit War and the Eleven Supernovas and the papers didn't cover him again.
Painful Transformation: Hody Jones underwent one after overdosing on Energy Steroids. Afterwards, Hody is seen as a bigger and much more powerful monster.
Papa Wolf: In this series, it might be easier to list the male characters that don't seem to have shades of this, as even the villians tend to fiercely guard their comrades and crewmembers (or at least the ones the judge valuable). For example:
Don't mess with any of Whitebeard's crew members. He'll storm into a heavily fortified Headquarters with all his divisions and all his allies, just to save one crewmember.
Luffy too. Hurt one of his friends, strangers he's never met or even your own crewmates, and you better be prepared to suffer a CRUSHING defeat.
Oh, you threatened someone's siblings so they'd work for you? You'll be fine, really, it's not like it's a Berserk Button for him ...
Zoro tends to be like this towards Chopper.
Or any allies, for that matter.
Brook. He's all fun until you try to kill one of his crewmates, then he'll send you straight to the afterlife. Or, more accurately, bring the afterlife to you.
Shanks is a slightly more laid back version. While he briefly freaked out when the bandit Higuma escaped with Luffy, he swam as fast as possible to save Luffy from a sea king, sacrificed his arm in the process, and while bleeding, glared/used Haki on said sea king to scare it off while holding Luffy with his remaining arm. One wonders what he would have done to Higuma if he had gotten there before the sea king ...
Garp is a Grandpa Wolf who was going to kill Akainu for causing Ace's death and he would have done so if Sengoku hadn't stopped him.
Fisher Tiger, he might be strict with his crewmates, might have hatred issues, but just remember he scaled a cliff to rescue several of them, and gave the World Nobles quite a black eye in the process.
Both Doflamingo brothers show this trait, from Doffy jumping out a window to get to Punk Hazard to check on what stopped Monet, to in a flashback brutally taking down a pirate that was going to hurt Kid!Baby 5 and Kid!Law; to Corazon/Rosiante trying to keep kids safe and away from his brother via Crueltobe Kind, to searching for a cure for Law's poisoning for six months, and consequently attacking every single hospital that refused to treat Law and made him cry.
Paper-Thin Disguise: Several throughout the series. The most noticeable cases include Usopp disguising himself as Sogeking, Foxy's various disguises, the fake Straw Hats, and Luffy's outfit in Dressrosa. Success varies.
Parental Abandonment: Seems to be the root of some daddy issues Ace has. He disowns his biological father and even goes so far as using his mother's surname, "Portgas".
Party Scattering: The Straw Hats are scattered across the world by Bartholomew Kuma and only come back together after the Time Skip.
Before the timeskip, the On Air Pirates are shown visiting an island on the New World that constantly rains lightning.
Also in Punk Hazard, a literal Hailfire Peaks, with one side covered in flames and lava eruptions, while the other is full of blizzards, and the center of the island has a perpetual typhoon due to the contrast of the temperatures.
Persecuted Intellectuals: In Robin's backstory, the scholars of Ohara got annihilated by the Marines because they pursue forbidden knowledge - specifically, that of the "Void Century" which the World Government refuses to tell at all costs. Since Robin was affiliated with them and managed to escape, she became a wanted criminal ever since she was 8.
Personality Swap: In chapter 661, Law uses his "room" to punch out the hearts of Nami, Sanji, Chopper and Franky. In the next instant, we see Nami talking like Sanji, Sanji talking like Chopper, Franky talking like Nami and Chopper talking like Franky. Yes, this really happened.
Some Paramecia type Devil Fruits can make the consumer this, the best example being Whitebeard who has the power to create shockwaves strong enough to destroy the world.
Princess Shirahoshi has the ability to summon and communicate with Sea Kings, a power if used incorrectly, could very well destroy islands. She isn't the first one to have this ability, as another mermaid princess had this power. Who was called Poseidon, the weapon that the Poneglygh of Shandora had described. So in essence, Shirahoshi is now the new Poseidon.
Pet the Dog: We know Smoker's not so bad after he buys ice-cream for a sad girl.
In chapter 650, a surprising one was revealed when Akainu spared Aokiji after winning their duel over who would be the next Fleet Admiral.
Phlebotinum: Devil Fruits, and to a lesser extent, Haki.
Dials were also this in the Skypeia arc.
Phlebotinum Overload: If a human were to eat two devil fruits, they would be destroyed instantly. Blackbeard managed to do exactly this and stole a second power from Whitebeard, with the help of his first power.
Pilot Movie: An OVA was released by Production I.G. a year before the Toei anime began airing, featuring a completely different voice cast and animation style.
Pint-Sized Powerhouse: Luffy. At 174 cm, he may seem like a bit too tall for the trope's standards, but in fact, 174 cm is tiny in the One Piece verse if you're not a child or an Innocent Bystander (and sometimes even then...). And Luffy is usually drawn in a style that makes him look much shorter than the actually is.
The Pirates Who Don't Do Anything: The Straw Hats don't actually do any pillaging. They are pirates In Name Only, and really just fun loving adventurers, who sometimes play the roles of heroes to people in trouble. They once tried to steal money from people they had helped out, but the "victims" were happy to pay them. Nami steals, but it's more of a compulsive habit she is at odds with, is usually Played for Laughs, and she is made sympathetic.
Planet of Hats: Amazon Lily: the isle of women. Also, Kamabakka Kingdom: the isle of transvestites.
And now, with Ace's death, Sabo, who's eaten the Flame Flame fruit.
Plot Tailored to the Party: Used quite a bit. Typically, each of the Straw Hats will manage to get paired off with an opponent that matches their abilities; Zoro goes head to head with swordsmen (or failing that, The Dragon), Sanji fights opponents who use martial arts.
Initially subverted in Enies Lobby: Kalifa's first opponent was Sanji, the Straw Hat who is least equipped to fight her. After he gets his butt kicked, Nami tags in, and lo, Nami's new weapon is the perfect counter for Kalifa's Devil Fruit.
Usopp generally subverts this by getting into fights with opponents that are quite a bit stronger than him (Chuu, Miss Merry Christmas and Mr 4, Jyabura), but then it's played straight on Thriller Bark where his cynicism makes him immune to Perona's powers.
Inverted in the third movie, where Sanji fights a swordsman and Zoro fights a kick-based martial artist. Of course, it's all a setup for an Aww, Look! They Really Do Respect Each Other moment when the two admit that their opponents' swordsmanship/martial arts aren't as good as "that person".
Also when Bartholomew Kuma separates them, they all go to the exact right island for them to be on in order to power up. Nami's on a weather island, Zoro's on Mihawk's private island, Chopper's in a land of advanced medicine, etc. Subverted a bit in that Kuma sent them there on purpose so that they could power up, because he's a good guy.
Plot-Triggering Death: The death of Gold Rogers lauches the Golden Age of Piracy, the setting of the story. Whitebeard's death, however, have caused things to take a turn for the worse.
Poke the Poodle: The Straw Hats' one attempt at actual piracy results in them stealing gold from people who consider it worthless and were already prepared to give it to them out of gratitude.
Actually, they were prepared to give them that PLUS a giant pillar made of pure gold and were left wondering why they left without it.
Possession Implies Mastery: It's unclear if this is the case for everyone, but in the Enies Lobby arc, Kaku and Kalifa are masters of their Devil Fruit powers by the time they need to fight, despite having had those powers for maybe a few hours.
Actually, it has been averted at times. When Teach got Newgate's earthquake power, it was made clear he needed to practice, and still couldn't defeat Sengoku immediately. Not long after, he avoided Akainu, saying he wasn't ready to face the Admiral yet.
Post Game Retaliation: In Dressrosa arc (specifically in the Corrida Colosseum tournament) after losing to Rebecca in the Round D match, the tournament losers tried to assault her when she's about to play in the next round. Fortunately, Diamante (the event organizer of the colosseum) stops them short, saying that Rebecca won by the rules.
Nico Robin from specializes in this, though (mostly since Time Skip) she has no problem to go up close and personal when needed. Her powers, from the Hana-Hana no Mi, lets her sprout copies of any of her body parts anywhere, from herself, the ground, walls of building, to people's bodies. She uses them mainly to strangle people from afar.
Trafalgar Law, with his Op-Op Fruit, can manipulate position of things within a radius, or "room", as if everyone around him are patients Strapped to an Operating Table. He rarely moves much from his position (aside from using hand gestures) while doing so. Downplayed, though, in that he's also a competent close-range fighter when the situation calls for it.
Discussed once - it's mentioned by Pekoms of Big Mom Pirates that LogiaFruit powers who practice this trope fully have short lifespans in the New World, because many fighters there employs Haki which, among other things, can bypass Logia's immunity to direct attacks.
Power Glows: A few examples here and there. A few of Zoro's attacks briefly manifest a glowing aura around himself (probably for dramatic effect), while Sanji's Diable Jambe technique has his whole foot glowing red-hot. Averted with Luffy's Gear Second technigue in manga illustrations, while the anime plays it straight by giving him flush skin and a shiny, sweaty sheen, possible as a visual Shout-Out to Goku's Kaioken technique.
Hey, Gear Second shares the same sound effect as Dragonball's, why not visual as well?
Power Levels: Bounties are an imperfect version of this, with Doriki being closer to accurate, but failing to account for things like Devil Fruit powers.
A more humorous version of this is Dosun's Verbal Tics.
Seastone as well. It nullifies Devil Fruit user's powers. Can be used offensively (for example, Smoker has a weapon tipped with it) but most often the Marines use it to restrain Devil Fruit users.
The Power of Friendship: The Straw Hats don't invoke this as much as you might expect from a group of true companions, although they do work together on occasion.
The Power of Rock: Brook has this after picking up a guitar and becoming the Soul King.
Power Perversion Potential: According to Oda, yeah, Robin can sprout extra breasts and Buggy's penis can fly. Same goes for Luffy who can stretch all, yes all his body parts (his penis). And in the recent manga chapters, one amazon mistook his penis for a stretchy mushroom.
Let's not forget Robin's persuasive tactics against Franky. How direct!
Several H mangas have taken advantage of Robin's potential as a one-woman orgy.
Powers via Possession: Luffy absorbed 100 shadows made solid by Gekko Moria from various people, including a highly proficient swordsman marine, and basically turned into a blue Hulk and could use all the skills and techniques of the people the shadows were from.
Protagonist-Centered Morality: Justified. The protagonists are pirates, so they don't care if someone does bad things unless It's Personal. If someone makes their friend cry, he's a bad guy (Arlong, Crocodile etc.) but if a bad guy helps them (Buggy, the same Crocodile) they are grateful. On the other hand they do understand that the marines are generally the good guys, but they get hostile treatment because their opposing standpoints.
Proud Warrior Race Guy: The Viking-inspired Giants from the island of Elbaf, itself described as a "Warrior's Paradise". Also Wiper, and the Shandian Warriors, inspired by Wiper's ancestor: Calgara.
Some of the Seven Warlords of the Sea are Psychos For Hire, especially the demented Donquixote Doflamingo. They've all proven they're a threat, so the Government made a deal with each one, freezing their bounties if they'd agree to only attack other pirates.
Public Secret Message: The main character returns to the scene of a major battle, ostensibly to honor the dead. Reporters on the scene photograph him, and his crew, scattered around the world, see the article, realize it isn't the kind of thing their captain typically does, and notice a simple message written on a tattoo.
Amusingly enough, the 12th opening shows Hannyabal and bunch of jailers doing what is unmistakably the Heil Hitler salute, just as the extremely cheery theme goes "Yay!"
Played frighteningly straight by Hodi Jones and his crew, whose extreme measures and fervent nationalism brought on by oppresion by racist humans mirror almost exactly the situation that brought about Nazi Germany. This only gets more obvious when in the latest chapter, Hodi's crew is seen getting people to declare their allegiance by stepping on a likeness of the late Queen's face, who advocated tolerance between humans and fishmen. This practice is a dead-on representation of Imperial Japan in the 1600, who got the Christians to renounce their faith by stepping on a likeness of Christ.
Pyrrhic Victory/Villainy: So how is winning the Whitebeard War going for you Marines? Numerous New World towns are basically damned, since they were under the protection of Whitebeard, and now that he's gone, the pirates in those towns finally were able to do whatever they want, like steal from and kill the people. Also, killing Whitebeard has resulted in a NEW age of piracy. The situation got so bad they had to move their headquarters to the second half of the Grand Line.
It backfired so spectacularly for then Fleet Admiral Sengoku, that he forced himself to resign along with Garp.
Though his resignation was also partially due to the fact that his superiors prevented him from effectively dealing with the situation in order to cover for their own incompetency.
The situation worsened to the point that the former Admiral Akainu, new Fleet Admiral Sakazuki was forced to institute a Conscription in order to make up for the losses during the war so they could contain it.