Take Me Instead: Both Zoro and Sanji offer themselves up to save Luffy from Kuma, resulting in one of the most powerful scenes of the series.
Actually Zoro offers himself up for Luffy, and Sanji tries to offer himself up for both Zoro and Luffy, but gets knocked out by him.
Take My Hand: Robin does this a lot with her powers whenever characters fall overboard or from other precarious places. Luffy and Nami attempt (and fail) this right before the latter is vanished by Kuma, and Luffy reaches out towards Ace in the anime's 10th opening.
Talking Animal: Chopper, of course. Justified in that he was a normal reindeer with a blue nose before he ate the Human-Human fruit.
Talking to Himself: During the reunion arc, Nami and Usopp are hassled by the fake Straw Hats, all are voiced by the same voice actors of the real Straw Hats though their voices are changed around (fake Luffy's voice is Sanji's, fake Nami is Chopper's, etc)
Talk to the Fist: In chapter 670, Clown begins to outline either his plan or the origins of Slime. Luffy simply jumps up into his face and grabs him.
Later on he begins to rant about how Luffy's a small fish and asks him if he's willing to take on his big name benefactors, clearly displaying both Small Name, Big Ego and willful ignorance of the outside world. Luffy's retort is to deck him and state that he's always fighting guys like that.
Tank Goodness: Franky brings one out to help fight off Hody Jones army.
Taught by Experience: The farther the Straw Hat Pirates have gone into the Grand Line, the more skilled, inventive and more powerful the group became. Unfortunately before the Time Skip, the curve went up a bit too steeply.
Tautological Templar: The World Government. Though if you've read/watched past the Enies Lobby arc, you probably already knew that.
Also Luffy and Usopp after Usopp rejoins the crew.
Brook cried when Luffy told him that Laboon was still alive and still waiting for him.
But....he's a skeleton...he doesn't have any tear ducts. YOHOHOHOHO!! SKULL JOKE!!
Luffy, Usopp and Chopper do that to anything mecha-related (e.g. laser beam, rockets, Humongous Mecha, etc.).
Teeth-Clenched Teamwork: Happens when Zoro and Sanji have to work together. Also, when Luffy, Buggy, Mr. 3, Crocodile, Mr. 1, Jinbei, and all of the other escaped inmates of Impel Down had to cooperate to try and save Ace.
Technicolor Toxin: Most of the toxin and venoms show onscreen are purple, including Magellan's venom, Musshuru's Spores and Crocodile's Hook. But there's also green poison (the Daft Green trees in the tenth movie) and oddly colored toxins like the MH 5 and Magellan's strongest attack.
Tempting Fate: After Franky recharges on cola and lets out the biggest SUUUUUUUUUPER thus far, the first words out of Fukuru's mouth are "You gonna hit me with another one of your weak punches (chapapa)?"
Tender Tears: Vivi and Franky. Both are highly emphatic and cry easily.
Terrible Trio: Toei is doing their darnedest to turn Foxy, Hamburg, and Porche into this in the anime... and have largely succeeded.
Also, Buggy is this to a degree in the manga.
Thanatos Gambit: Roger turned himself in to the World Government, and then reversed their intended effect of his execution with his last words. What was intended to be a lesson to all pirates ended up causing an Age of Piracy, arguably making the entire series a Thanatos Gambit.
Whitebeard decided to turn his death into one by confirming the treasure is real, erasing doubts of its falsehood and starting the whole thing all over again.
Theme Naming: The Seven Warlords of the Sea are all named after animals, many women are named after birds, and everyone on Amazon Lily is named after a flower.
There's also Gold Roger and Rouge, both named after the Jolly Roger (or the French version jolie rouge, in Rouge's case).
Gold Roger and Silvers Rayleigh also count.
It isn't just characters: the art books and data books also have their own naming themes going on. Color Walk 3, 4, and 5 are named after animals that "rule" their respective habitat (Lion, Eagle, Shark), while the data books are Color-Coded for Your Convenience (Red, Blue, Yellow, Green).
There Can Be Only One: In chapter 634, after Hody starts to talk about what his plans are, he talks about being pirate king. At which point Luffy takes out half of his gang of pirates and tells Hody that there can be only one pirate king.
There Is No Kill Like Overkill: Doubles with Disproportionate Retribution: A group of scholars from a certain island is studying the Void Century, something the World Government deems a serious crime. Akainu's solution: blow the island and all its inhabitants (not just the scholars) to kingdom come. Even Aokiji, who isn't exactly soft himself, thought this was overkill.
A little elaboration on this — the plan was originally to blow up the island with the scholars on it. The other citizens had already been evacuated on another ship. However, Akainu (then known as Vice-Admiral Sakazuki) then blew up the evacuation ship, just on the off chance that one scholar managed to get on board. Not only was Aokiji (then known as Vice-Admiral Kuzan) disgusted, but it also stunned Spandine, the JerkassGeneral Failure of CP9 and the father of Spandam, who ordered the evacuation.
The attack that was used on Ohara is in itself overkill: the Buster Call. It uses a fleet of ten battleships commanded by five vice-admirals to utterly destroy one island — and the attack will not discriminate. It can and will destroy entire populations without thought, and it is the strongest attack commandeered by the marines on a single target. It's sheer destructiveness means it is used as sparingly as possible, and can only be ordered by ten people in the world: the three admirals, the Fleet Admiral, the Commander-in-Chief, and the Five Elder Stars. The only way a person that is outside of that small group of people can order a Buster Call is if they are given the authority to do so by one of the group, via giving them their golden den den mushi.
There Was a Door: Garp went of his way to smash through the wall of the home the Straw Hats were in simply to punch Luffy in the head. When his own subordinates ask why he would not simply go through the door, he simply said "It was cooler". At least he was polite enough to help repair the wall.
Third Time's The Charm: Luffy's fights against Crocodile. He lost the first two, and took him down in round 3.
This Cannot Be!: Don Krieg doesn't take too well to getting beaten by Luffy and in response repeatedly shrieks that no one can defeat him.
This Is Something He's Got to Do Himself: Luffy takes this attitude during Zoro's duel with Mihawk. When Johnny and Yosaku attempt to intervene, Luffy holds them back and tells them to wait until the end, despite obviously wanting to help Zoro himself.
Similarly averted when Franky found out that the Straw Hats pulled this exact trope on the Franky Family and even said the words "This is unforgivable, Straw Hat!", almost turning into a Cycle of Revenge. However, a series of circumstances allowed the Straw Hats and the Franky Family to work together, and in the end, Franky even pulled a Heel-Face Turn, and joined the Straw Hats.
Franky and Iceburg have this towards each other, though both are eventual subversions. Iceburg blames Franky for enabling Tom's Frame-Up and imprisonment, but admits that, forgiveness or no, he is still happy Franky isn't dead. He later lets go when he realizes that Franky blames himself for what happened more than he does anyway. Franky is outraged Iceburg would go to work for the World Government, who were the ones who actually did the framing and imprisoning, but later acknowledges that Iceburg having connections was really the only thing keeping the Government from doing to him what they did to Tom.
Title Drop: Since the name of the manga is also the name of the ultimate treasure, this happens every so often.
Together in Death: We have Gold Roger and his lover, Rouge. In some ways, we could consider Whitebeard and Ace in a platonic sense, seeing what the former went through in order to rescue the latter.
Token Good Teammate: The Seven Warlords can be cruel, selfish, amoral or a Jerk Ass ... save for Jinbe who only took his position to protect Fishmen Island and build up a better relationship between merpeople and humans. And also Kuma, who worked as a double agent for the Revolutionaries.
Hatchan was the least cruel of the Arlong Pirates and he would later become an ally to the Straw Hats.
Too Dumb to Live: Usopp jumped off the ship... while they were in the sea of clouds. Needless to say, he almost went splat.
Though, one should remember it was a sea of clouds that was capable of supporting their ship.
Actually Luffy, Brook, and Chopper have their moments. If they see the other drowning, they will jump in to save them, despite the fact they know they can't swim.
Also, Gedatsu deserves a mention here. He's so forgetful that at one point, he was thinking something at one of the Straw Hats only to realize that he was thinking it and that his mouth was closed. He has also forgotten to breathe, which could've led to this trope being literal, had it continued.
The World Nobles count, to an extent. They are utterly incapable of understanding that their downright reprehensible behavior tends to make them universally despised, and the "common" people absolutely will kill them if given half a chance to do so. One even had the nerve to insult a group of former-slave Fishmen on their island when they were armed, and he was alone, injured, and had no way of contacting the Admirals that normally keep people from delivering their long-deserved comeuppance. Would have undoubtedly gotten the dumbass killed, had Queen Otohime herself not stepped in.
Did Demalo Black, who only had a 26-million-beli bounty, really think he could impersonate the 400-million-beli-bounty Luffy and NOT have Sentoumaru come with TWO Pacifistas to kick his ass?
Sentoumaru: STRAW HAT ISN'T SOME PIECE OF TRASH LIKE YOU!!!
Then there's Coby and Helmeppo. Hard to believe that the former was a chubby cry baby and was much shorter than we see him now, and the other was a Smug Snake idiot son, of one of the story's earliest (and perhaps most inefficient) Big Bad.
And after the two year skip, all of the Straw Hats took a level in badass. Luffy mastered Haki, Zoro significantly increased his ability with swords, Sanji can run at super speeds on land, underwater, and through the air as well as improved combat abilities, Usopp becomes incredibly buff and masters Pop Greens, Nami has mastered weather control, Chopper has mastered his shapeshifting and his forms have become more powerful, Robin can now generate clones of herself and giant limbs, Franky made himself a new and more powerful body as well as a mech, and Brook gained enhanced musical abilities as well as master over his devil fruit to the point where he can leave his body similar to astral projection and put his bones back together as long as the bones themselves aren't damaged.
Touch Telepathy: Violet normally doesn't have to be really close to another person to read his/her mind with her powers, but in order to let someone else read her mind, that someone should look at her eye through her circled thumb and pointer finger.
Transvestite: Mr. 2 Bon Clay and the natives of Kamabakka Kingdom.
Trap Is the Only Option: In the Dressrosa Arc, Franky realizes right away that it's no coincidence Ace's Mera Mera fruit is being offered as a prize at the Colosseum right when Luffy shows up on the island. But the prize has high sentimental value to Luffy, and Franky knows trying would be better than having Luffy regret losing the chance to get it. Besides, it's their only chance to find out the location of the Smiles factory.
Treasure Map: Sometimes comes up, thought not as often as you'd think for pirates.
Treachery Cover Up: When news got out that Crocodile had his sandy ass handed to him, the World Government credited the defeat to Smoker. Who, by the way, was less than happy about it.
Troubled Backstory Flashback: Most of the Straw Hat crew's flashback depict a (relatively) happier time before everything goes to hell. The post-Paramount War flashbacks for Ace, Luffy, and Sabo might very well be there just to wrench the stake further into the gaping wound in most fans hearts.
Trouser Space: You would think that Spandam might be a little hesitant to take blueprints that Franky probably kept in his speedo.
Wordof God says that Franky keeps his tools in his speedo.
In the G-8 filler arc, Luffy pulled the octoballoon from the end of Skypiea from his trousers.
Zoro: Yeah, but...didn't it feel weird down there? Luffy: Down where?
True Companions: (Former Trope Namer when the trope was named for a mistranslated Japanese word). The heart and soul of the story. Luffy, especially, lives and breathes this trope.
Whitebeard, all the way. For the World's Strongest Man, who could have had anything, anything, this world had to offer... this is all he ever wanted. He succeeded.
Trust Me, I'm an X: Trafalgar Law tends to announce his profession with such a line. Though, it doesn't help that, in addition to being a doctor, he's a pirate. And, OH YEAH, his moniker is "Surgeon of Death," so you might not want to trust this guy too much.
Turns out he's actually pretty good at his trade. Good enough to save Luffy and Jinbe, who are respectively a human and a fishman, from the brink of death.
Truth in Television: Hordy Jones joined the Neptune Army just to learn fighting skills so he could wage war against the humans. There are actually several white supremacists in the US who join the army in order to prepare for a supposedly upcoming race war.
Until the cover of chapter 666, that is. Turns out he escaped somehow and now runs level 5.5.
Unexpected Character: Bellamy's appearance in the Dressrosa arc took the fandom completely by surprise, since everybody had written him off as dead years ago. Similarly, the appearance of Jesus Burgess in that same arc also stunned the audience, in-universe and out.
Unexplained Recovery: It's amazing what kind of things that people in this series go through, yet still live to tell the tale. For instance: Pell carrying a bomb out of the clock tower, seemingly getting blown up when it goes off, and still ends coming back just fine.
Unfortunate Item Swap: Spandam mixes up his two snailphones, accidentally issuing a buster call ("Something has Gone Horribly Wrong here, level the place with heavy artillery, take no further orders from this phone") on his location.
Ungrateful Bastard: Shiki at the start of One Piece Film: Strong World. Granted he was already a prick to begin with, but the Straw Hats go out of their way to warn him and his crew incoming of an typhoon that not even his weather staff can predict. After they avoid it, how does he show his gratitude? By kidnapping Nami and nearly killing the crew by dropping them dozen of feet from the air. Big mistake.
Done much earlier by Don Krieg, who attacks the restaurant that just saved both his and his crews' lives.
The Longarm Tribesmen who Brook decides to willingly work for during the timeskip repay him by trying to turn him over to the Marines when he tells them he plans on retiring.
Much like Shiki earlier, Z from the twelvth movie is saved by the Straw Hats, who found him drifting across the sea and tended to his wounds. How does Z thank them ? By attacking them the second he learns they are pirates. Then again, considering his past, who can blame him ? The last time he showed mercy to a pirate, the asshole came back, cut his arm, and slaughtered his entire division. Note also that he was actually quite grateful for the save, until he learned they were pirates..
Universal Poison: Averted with Magellan. His Doku-Doku no Mi gives him command over all poisons, running the gamut from minor irritants to paralytic agents to full-on stone-melting corrosives. Even with antidotes for some individual poisons, once he hits you with lethal doses of about a dozen different poisons you're beyond the help of medical science. Luffy found out the hard way that Magellan's poison wasn't just a Standard Status Effect he could Determinator his way through.
The Unreveal: Happens whenever information about One Piece or the Will of D is about to be revealed. When Usopp asks Silvers Rayleigh what's on Raftel, Luffy basically says NO SPOILERS. Later, Whitebeard flashes back to a conversation he had with Roger concerning the true nature of the Will of D, but the flashback is cut off and Whitebeard dies a few pages later.
Unskilled, but Strong: Luffy's defeat of Sandersonia and Marigold falls into this. Luffy couldn't get past the Boa sisters' Haki abilities until he went to Gear 2nd and became faster than Sandersonia could follow even while reading him and stronger than Marigold's defenses could handle.
Unsound Effect: When Wapol's crew is stared down by a bunch of Lapins, the sound effect is LAPIN.
Unstoppable Rage: Numerous times by most of the Straw Hats, but the most hilarious is when Sanji finds out that Absalom is about to marry Nami and has seen her naked. He becomes so angry he starts burning - literally.
Sanji again anytime he remembers the "Hell" he went through the past two years, even enough to set his whole body on fire instantly.
Unwitting Pawn: Both the Whitebeard Pirates and the World Government are patsies for Blackbeard, the man who single-handedly caused what is confirmed to have been the biggest battle in recorded history, got what he wanted, and escaped scot free.
Up Through the Ranks: Implied by a colorspread page showing a shot of many of the current (and some ex) high ranking Marines' younger selves as foot soldiers.
Upper-Class Twit: The Celestial Dragons. They're the descendants of the people who created the World Government, so they feel that they don't have to do anything. That includes not breathing the same air everyone else is breathing.
Use Your Head: Luffy has done this at least twice. One time, he used his head to stretch back and hit Captain Kuro;knocking him out. Another was in Skypeia when he used gomu-gomu bell, which is him using his head as a weapon.
Verbal Tic: Too many characters to list, and the unique laughs for characters are practically a whole subtrope.
Villain Ball: The World Government is a Well-Intentioned Extremist government and 9/10 of their acts are to protect the citizens and the World peace with a Kick the Dogmoment... then they decide to start a war with Whitebeard, one of the Emperors to take down the last vestige of Roger and to show they are not afraid of pirates. The results were... mixed.
Villain Episode: Cover arc Buggy's Crew: After the Battle!, Jango's Dance Paradise (showing how did the Black Cat pirate become a marine), Hatchan's Sea-Floor Stroll, Wapol's Omnivorous Hurrah, Gedatsu's Accidental Blue-Sea Life, Miss Goldenweek's Operation: "Meet Baroque Works" (showing how did the Baroque Works agents end up in Impel Down), Enel's Great Space Operations, and CP9 Independent Report.
Villain Forgot to Level Grind: Remember those Pacifistas that utterly demolished the Straw Hats and a large chunk of Whitebeard's forces? Remember when defeating the first one left the entire Straw Hat crew completely drained and vulnerable? After the time skip, Luffy, Zoro, and Sanji are all capable of effortlessly bringing them down. Though it's stated that there are newer models.
Villain Respect: Four examples over the course of the story, all toward Luffy. Mihawk, remarks positively on Luffy's determination and drive to become Pirate King (note that while Mihawk isn't a villain in the correct sense of the term, he is a member of the Shichibukai, which technically makes him an enemy to all pirates, including the Straw Hats.) Enel compliments Luffy's drive to become Pirate King, the "ruler of the entire blue ocean;" Rob Lucci compliments Luffy's leadership skills in stark contrast to Spandam; and Blackbeard encourages him to pursue his dreams no matter what.
Villainous Breakdown: Crocodile and Moria had really epic ones. Also Spandam, though his multi-stage breakdown was pathetic rather than frightening.
Let's face it. Every enemy Luffy initially fights goes through one. He has that effect on them.
Villainous Rescue: Granted, they were already in an Enemy Mine situation, but it's still surprising when chapter 578 comes around and CROCODILE of all people steps in to save Luffy.
Villains Out Shopping: The post-Paramount War chapter covers place some of the more serious and/or villain characters into lighthearted scenarios, such as Magellan fishing with Hannyabal, Impel Down sadist Sadie-chan eating out with the head guard Domino, Mihawk eating takoyaki with Jinbe, and Akainu tending to a bonsai tree.
Also Caesar Clown, or 'The Master' from Punk Hazard. The few people on the island see him as their kind saviour when he really doesn't give a damn about any of them, and is completely willing to sacrifice their lives or kill them outright for his dangerous and insane experiments. He also is experimenting with turning children into giant soldiers, knowing they will die from it within a few years, while the children see him as the helpful doctor who's going to cure their "disease" and return them home.
Vitriolic Best Buds: Zoro and Sanji, obviously. When they meet up again after not seeing other for two years, the first thing they do is insult each other. Making it seem more like they had been apart for two minutes than two years.
Vocal Dissonance: Noticeable with characters like Chopper in his combat forms, Miss Monday, and Fukuro.
Wacky Wayside Tribe: Filler uses this now and again, to give a side-voyage for the anime while the manga gets ahead. In canon, the just-introduced Kuja Tribe on the island of Amazon Lily already appears to fit the trope to a T.
Subverted. The leader of the Kuja, Empress Boa Hancock, turns out to be a Warlord of the Sea and a plot coupon to help Luffy infiltrate Impel Down. The Amazons have since become another one of Luffy's allies, especially since Hancock has developed an intense crush on Luffy.
Skypiea was considered such for a while due to its irrelevance towards the series main plot before it became clear that there was really a massive amount of Foreshadowing in it, including but not limited to Haki, Posedion, Blackbeard's rise to power, Doflamingo's "New Age" and Rogers' crew having uncovered the true history.
Wanted Poster: Considered De factoPower Levels on the Grand Line by the general public. The higher a person's bounty, the stronger and/or more dangerous to the world s/he is.
War Arc: The Whitebeard War had an entire saga named after it, but most of the major fighting occurred in the Battle of Marineford arc. Its participants included the Whitebeard Pirate Crew, the Marines, the Seven Warlords of the Sea and Luffy.
Was Once a Man: The sentient toys on Dressrosa were once humans but turned because of a Devil Fruit power. Generally speaking those close to the victim not only don't recognize or believe the victim, they forget the victim even existed.
Wave Motion Gun: The Thousand Sunny's Gaon Cannon. Not every day you see one of these things on a pirate sloop.
We Want Our Jerk Back: Usopp, Sanji, and Franky were notorious troublemakers in their respective home towns. When Usopp left the entire town was thrown out of sorts by the absence of his pranks and we see that some had even taking to using him as an impromptu alarm clock. Sanji is outright attacked on his way out the door by people who are tearfully bidding goodbye seconds later. When Franky was leaving members of the crowd watching called for him to return soon.
Weak, but Skilled: Usopp and Nami in particular, using gadgets and tactics in their battles. Robin should also count as far as Devil Fruit powers go, since she isn't physically any stronger than a normal person, but her power lets her use leverage and devestating creativity against her foes.
Weak-Willed: Luffy is highly susceptible to hypnosis. He can even be affected by hypnosis that isn't even aimed at him. He also repeatedly fell victim to Miss Goldenweek's Colors Trap.
Webcomic Time: One Piece began on August 4, 1997, and to date, on-screen action covers less than a year of story.
Well-Intentioned Extremist: The Marines down to a T. Aokiji, Smoker and Hannyabal for example are basically good persons who want to protect the innocent from pirates while others like Akainu and Sengoku are far more brutal and merciless in their quest for peace but Sengoku was outraged that the escape of the prisoners from Level Six was covered to the point of resigning and Akainu was ready to tackle Whitebeard for the Marines and continue after being pummeled half to death so the "peace of the world" can reign . Luffy is the same, ready to help others at the drop of a hat but though nothing of letting some of the most degenerated individuals in the planet free as long it saved Ace and acting with what he believes is right, regardless of morality, factions or consequences.
There's also Ohm, who just wants to save everybody from fighting and ruining the inherent happiness they were born with...by killing everybody so they can no longer suffer.
After teasing the idea of becoming a full-time Straw Hat, Vivi suddenly, and unexpectedly to anyone, including the readers, shuts the idea down to her crew as they ready to pick her up, in one huge line:
"I choose to stay!"
Kaku gives some very unpleasant news when the Straw Hats ask about the Going Merry.
Kaku: I'm going to give it to you straight. Your ship......can't be fixed! Not even with our skills!
Another one from Chapter 550:
Sengoku: The truth is...Portgas D. Ace: your father is Gold Roger!
And before that, in Robin's flashback, they fire on a passenger ship full of innocents just in case a archeologist hid on board.
Coby called everyone present out on this at the end of the war when the marines were fighting against fleeing and deranged pirates while injured soldiers could still be saved.
What Does This Button Do?: While running from angry locals after landing on a winter island, Franky comes across a large button with a skull on it. Thinking that it's a pirate symbol, he presses it. As you might have guessed, that's not what the skull was a symbol for.
What If?: The question poised for the 9th One Piece movie: Episode of Chopper, which panned out a little differently than from the original story.
What the Hell, Hero?: Hannyabal gives one to Luffy in Impel Down, pointing out that many of the prisoners his group has freed deserve to be locked away, as they would otherwise be terrorizing innocent people. Case in point: Crocodile. In response, Luffy continued to insist that Hannyabal get out of the way. Opinions vary (his brother's life was at stake, not to mention his own), but for many this was a shocking turn for Luffy. Possibly done to create a parallel between Luffy and Blackbeard.
Though in Luffy's case, it should be noted that he did not originally want to free Crocodile. It was Emporio Ivankov who conviced him to do it.
Incidentally, Sengoku gives (or rather wants to give) one in 581. When he finds out the World Government is going to cover up the escape of a ton of Level 6 prisoners rather than warn the public and admit their failure, he rightly shouts "Are you fucking kidding me?!"
What The Hell, Townspeople?: This happens at least once in the course of the story, but no more obviously than in the Fishman Island arc, where Koala is returned to her town by Tiger promising to tell them about how they are good people, only to have the other townspeople sell them out to the Navy moments upon arrival in chapter 623. To make matters worse, her own mother hides the truth from her.
Though it should be noted that the Marines were threatening to take Koala back into slavery, so they really didn't have much of a choice.
When All You Have Is a Hammer: Every Devil Fruit users' power is a "hammer" as the power never grows stronger or weaker. The users must think of ways to use this power in new ways. Special mention goes to Luffy because while he is an idiot, he comes up with surprisingly creative ways to use his "hammer".
The Five Elder Stars, but there is no real oversight at any level. They are free to do what they want.
Whole Episode Flashback: In the Skypeia arc this took three whole episodes and it was of the tale of the ancient past, anyway, and in the Enies Lobby arc, it took two episodes and a double-bill special flashback.
Why Couldn't You Be Different?: A major point of contention between Garp and his grandsons is their decisions to become pirates instead of marines like he wished. Ultimately, however, that was only out of the desire to protect them. Regardless of the fact that they are world-class criminals, he has always been proud of them, knowing that he raised them to be good people.
Widely-Spaced Jail Bars: In one episode, some characters are caught in a net. In closeup shots the net has a very fine mesh, but in distance shots the mesh is drawn wide enough that the characters could potentially fall right through. This demonstrates that it's done for the visual necessity of drawing the trap in a way that doesn't obscure the characters.
The inhabitants of Merveille have feathers growing out of their forearms, though they themselves don't know why or how. After Shiki's defeat and the return of their island to the sea, they discover that they can indeed fly.
Not to mention the Skypeians, Bilkans, and Shandians, despite all of them originally coming from the moon. They're small and seem to be purely cosmetic, though.
Nico Robin can also use her Devil Fruit power to pull this off... but only for about 2 minutes, and it's apparently very exhausting (since it consists of pulling together about a coupla' hundred arms in the shape of a pair of wings and then FLAPPING them), so she very rarely uses it. Thriller Bark, when caught on a collapsing bridge, was the first time.
With Friends Like These...: Usually, the only time that Zoro and Sanji are not fighting each other is when there's something or someone that has gotten in the way of them fighting each other.
A Wizard Did It: The majority of the Devil Fruit powers seem to violate major, established laws of physics and causality, but that's okay because they're magical. Also it's cool.
Women Are Wiser: Played straight with the female members in the Straw Hat crew. Although at times, they might be Not so Above It All (primarily Nami), they're still much more rational than their fellow male counterparts.
Averted for the women in Kuja island though. They're just as barbaric and savage as several other islands. Just like the male Marines, they also gawk at Hancock and forgive her for evil acts simply because she's beautiful. When Luffy gets angry at Hancock, they cheer for his execution, despite the fact that he got angry because Hancock turned her own citizens to stone over an honest mistake.
Women Drivers: Averted with Nami in Skypeia. She picks up a waver and ends up getting the hang of it within minutes. This is after Conis told her that it usually takes someone about ten years to master using it.
Won't Take "Yes" for an Answer: Luffy keeps trying to attack Aokiji to keep him from arresting Robin, despite Aokiji repeatedly telling him he has no interest in bringing Robin in.
Diving to Fishman Island, and seeing the giant Yarikiman Mangrove roots from underwater.
World of Badass: One Piece is capable of, among other things, making chefs, carpenters, and even crossdressing queer ballerinas absolutely, unarguably, BADASS. That last one manages to pull off arguably one of most badass scenes of all in a World of Badass.
Attack names (most of Zoro's sword moves, notably, also resemble types of sushi when written), character names, and in the seventh movie over half the lines of the plot-central prophecy were puns.
The Zoro/Kaku fight in Enies Lobby is brimming with all kinds of weird puns.
At the beginning of the Sabaody Arcapelago arc, when Duval's crew attacks the Thousand Sunny, they keep talking about keeping their flying fish in formation. The problem is, in Japanese, the word for "formation" is hentai, which also means "pervert". Naturally, Franky answers to this.
The Worf Effect: In full swing during the Marineford arc. Whitebeard, Jozu, and Marco easily repel the initial moves of Aokiji, Mihawk, and Kizaru respectively. The latter three all curb-stomped the Straw Hats. Three out of Seven Warlords quickly bring down Oars, Jr., whose ancestor's reanimated corpse nearly defeated the Straw Hats.
All the giants present in Marineford serve as prime examples for this, serving as fist-fodder for Oars Jr., Whitebeard and Luffy, in that order.
CP9 did this to the Galley La foremen hardcore.
The Demon Guards from the Impel Down arc seem to exist solely for the purpose of being clobbered by Luffy, Crocodile, or Jinbe every time they show up, the second time off-panel.
And after the timeskip, the Pacifistas have become textbook examples.
At least the older models.
The New Fishman Pirates were used like this to show just how strong the entire crew has gotten in the last two years.
Robin was on the verge of giving up on her life until Luffy came along. Her time with the Straw Hats was the happiest she had ever been, and they literally are the only people in the world she cares about. But even then, she still believed that despite their kindness, they would still eventually abandon her because her enemies amounted to the entire world. It was only when they declared war on the world itself in her name that she realized that she had finally found her place.
Ace's angst over his bloodline was so great that the only reason he bothered to keep on living was to find out whether or not he deserved to be born. It only stopped being so painful when his brothers, and eventually, the Whitebeard Pirates, came into his life. All of this only serves to make his death more tragic.
Luffy's Heroic BSOD after Ace's death was so bad that he was on the verge of crossing the Despair Event Horizon. When he was at his absolute lowest, the only reason he chose to keep on living was the realization that he still had his crew.
Wretched Hive: The Sabaody Archipelego. With all of the bounty hunters, human shops, ship-coating ripoff bars, Celestial Dragons who come by every so often, the auctions of people/mermaids and the marine base being right next door, it's a wonder that any pirate rookies who get there ever make it through to the New World.
Mock Town is a deconstruction. Sure pirates run roughshod all over but they refrain from attacking the townsfolk, if only to have people who can sell them food and booze. Also, since pirates spend money like water Mock Town's economy is booming.
Written by the Winners: Donquixote Doflamingo basically says that whoever wins the war between the marines and the pirates becomes justice.
Averted with the poneglyphs. Which, according to Professor Clover, were probably written by the losers of the war that happened during the Void Century.
That's probably more played straight, considering the World Government have successfully wiped out nearly everyone capable of reading them.
Xanatos Gambit: Blackbeard. Doesn't matter if Luffy escapes and Ace shows up; he'll just capture the latter instead. Doesn't matter if he loses his Warlord status; he only wanted it to get into Impel Down anyway. Doesn't matter if Magellan curb-stomps him and his entire crew; he's convinced someone to bring him the antidote. Doesn't matter if Shanks stops him from sinking Marineford; he got what he wanted ( dead Whitebeard, earthquake powers) and said what he needed to say. ("Dear Everybody: You're FUCKED.")
Gambit Roulette: It's important to remember just how completely insane Blackbeard's gambit was based soley on how lucky he got. The astronomical number of factors that could have killed his entire plan is just dizzying. First of all, if Luffy hadn't been in Impel Down around the same time as him, then Magellan wouldn't have been inconvenienced enough to release Shilew; which would've resulted in him being hopelessly curbstomped by Magellan, with no one to help him. Luffy even getting into the prison relied on the actions of both Kuma and Hancock; two people he no control whatsoever over. Taking Ace instead of Luffy was the entire reason he was able to get past the Impel Down phase of his plan, since it's made quite obvious that he wouldn't stand a lick of a chance against Whitebeard under normal circumstances. The war resulting from Ace's execution weakened Whitebeard just barely enough so he make the kill.
He is convinced that it is fate.
Xanatos Speed Chess: Blackbeard's proven highly adept at improvisation. He initially targets Luffy as his ticket into the Warlords, but goes for Ace when the opportunity comes along. Faced with a probable enemy right on the gates of Impel Down, Blackbeard up and recruits him.
X Marks the Hero: After the time-skip, we see that Luffy now has an X shaped scar on his chest.
Year Zero: Many characters refer to the current era as having begun with Roger's death, and with the newest era beginning with Whitebeard's death. Though the official Year Zero appears to be the creation of the World Government / end of the Blank Century eight hundred years prior.
Whitebeard & Crew and Luffy to Ace during the Impel Down/Marineford Arc.
You Cannot Kill an Idea: Roger suggesting that people go and try to find his treasure is a good one. Hiruluk saying he will be remembered is another. The newest one so far is when right before Whitebeard dies, he says that One Piece is still out there. Thus pretty much creating the "silver" age of piracy.
You Didn't Ask: The reason Luffy never told anyone about his strange family tree and about why Ace is his older brother. Though to be fair, he himself didn't know he even had a father until Garp told him and everyone else, so he couldn't have told them about that.
You Gotta Have Blue Hair: Buggy, Tashigi, Vivi, Ms. Doublefinger, Franky, Iceburg, Ivankov, Nojiko, Ain... did we miss anybody?
Strangely, Zoro (with his green hair) is the only one in the series whose hair color is ever treated as abnormal.
You Have Failed Me: The fate of any Baroque Works agent who fails their mission. Mr. 3 got better.
You Have No Idea Who You're Dealing With: The Imposter Straw Hats had no idea that the people they were after for humiliating them were members of the real Straw Hats, included Luffy. Their reaction to learning Luffy's true identity wasn't subtle, that's for sure.
Up until the crew met Aokiji, none of the Straw Hats except Robin fully understood just how powerful the Marines' top people could be and how far Luffy and others had to go before even remotely standing a chance against one third of the "Greatest Military Powers".
Caesar Clown said it as part of his Hannibal Lecture to Luffy : Because Caesar has connections with Doflamingo, who himself has connections with one of the Four Emperors, laying a hand on Caesar would be, in his opinion, suicidal.Luffy kicks his ass anyway.
You RebelPirate Scum: Quoted mostly by members of CP9, but a common sentiment among World Government personnel.
"You're Not My Type": Played for Laughs in Fishman Island. Mermaid Princess Shirahoshi says this is the reason that she won't marry Vander Decken. Considering that he's been using his devil fruit power to throw any object he can at her (from literally anywhere) for ten years, forcing her to hide away in her castle out of fear, practically everyone is surprised this is her main concern.
The first time Urouge bulks up he utterly dwarfs Hawkins, yet shrinks down a bit for subsequent appearances.
On one volume cover Mr. 2 is shown to be a little taller than Crocodile, who's over eight feet tall, but isn't shown to be anywhere near that height in the manga itself.
Then there's the infamous "Giant Warlords" spread, where Mihawk and Hancock, both confirmed to be no taller than six and a half feet, utterly dwarf a marine soldier talkng to them.
Even Gecko Moria, who is over 22 feet tall, suffered from this. When he first appeared, he looked more like a giant than an abnormally large human.
It didn't help that the minions that he first appeared next too are like 1 foot tall so perspective was shot to hell and back.
Luffy. At the start of the series, his height was somewhat average, at least among civilians (he was and is always shorter than his opponents, but that's probably to make him kicking their asses even more impressing). Nowadays, Art Evolution has made him a midget, who is dwarfed by most civilians and ridiculously dwarfed by his opponents. He even seems a head shorter than Nami, despite that he is supposed to be 5'8, and Nami is 5'6.
This exact line was later used again by Vice Admiral John Giant on Whitebeard, who subverted it by launching John across the island.
And now Garp has done this to stop Luffy from getting to Ace! Yet again subverted, because in the end he throws the fight.
Lampshaded by Rob Lucci:
Luffy: What was it just now?! Where was Robin speaking from?!
Lucci: Behind this door.
Luffy rushes the door; Lucci intercepts him.
Lucci: "I can't let you pass." At least let me say that.
That particular instance is an unusual example in that both sides are trying to get past the other (to rescue Robin/kill the rest of the Straw Hats) and their goals require the other guy to be defeated, not just passed.
Franky attempts to stop the Puffing Tom from taking Tom to Enies Lobby and says this.
Zany Scheme: Silvers Rayleigh had one that eventually lead into the two year time skip.
Zerg Rush: Don Krieg's pirates claim they're the strongest in the East Blue. Luffy informs them that they aren't strong, "There's just so many of you."
Also a key element to Enies Lobby's defense is its 10,000 man garrison.
The tactic is also downright useless in both halves of the Grand Line. Case and point: the armada of Don Krieg. With fifty ships and five thousand men, East Blue calls it an invasion force. The Grand Line calls it target practice. And this is in the first half, which is nominally called by everyone as Paradise.
In the New World, it's useless because many of the most powerful captains have an ability called Haki of the Conquering King, where one can impose their will upon others, and, if their will is weak enough, knock them out. During the Fishman Island arc, Luffy used this ability to knockout 50,000Mooks (which is ten times the size of Don Krieg's armada) in one blast — and the only reason he didn't knock out the other 50,000 is because his crew needed someone to fight.
Zombie Gait: Averted; most of the zombies are of average speed and intelligence, have distinct personalities, and can even disobey their masters in some instances. Justified by the fact that these zombies actually have "souls"... just not their own.
The aversion is lampshaded when Nami, Usopp and Chopper openly expect the zombies to be slow as per cliche, and then are shocked when the zombies dash at them.