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One Piece has many dramatic, emotional and funny moments, but sometimes some of their impact is lost in the execution.
When Usopp duels Luffy over the Going Merry, one of the most tragic moments in the series, he gives every indication that, despite being the weakest member of the crew, he knows how he fights and is going to put everything he has into the duel. He then makes his first moves... boasting about having 8,000 followers and using "Usopp Spell" to make Luffy imagine himself in terrible pain. Granted, many of Usopp's techniques (especially those used in the duel) are used to make the enemy underestimate him while hiding their true effect, but the comically unbelievable lies felt out of place.
The bit about the followers is an Ironic Echo of their first meeting; viewers who didn't see their first meeting, however, will still be amused.
Episodes 404 and 405, in which Kuma arrives and teleports all the Straw Hats away from their losing battle with Kizaru, Sentoumaru and the Pacifista, lose some of the drama with the sometimes Off Model animation and the tendency of the Straw Hats to stare at what's happening with their mouths gaping wide open.
In the same episodes, upon realizing that he failed to save any of his Nakama, Luffy proceeds to bang his head on the ground and kick his feet in the air like a little boy being denied a lollipop. Needless to say, it's... uh... moving?◊
In the anime, whenever Ace is visibly shocked or disturbed by the goings-on throughout the Marineford Arc, he utters a bizarre "kkkkgkkkgk" grunt.
A lot of characters do this for some reason.
And then when he dies in the anime, he goes splat on the ground.
Marco's Big Bird-esque legs when attacking Akainu.
One Piece is usually good with tearful goodbyes... except the one Sanji gave to his friends at the restaurant when leaving to join the Strawhat crew, in which he shouts "GOODBYE, YOU CRAP GUYS!" while crying. Arguably, Narm Charm.
"And as for cannonballs, the cannonballs Whitebeard withstood are 46." That's two twenty-threes. And That's Terrible.
The depictions of crying, shouting or shocked people in One Piece are this. For the first, the characters usually have lots of snot running out their noses when they cry. Though it ruins the usual "romantic" depiction in fiction of a crying person, especially a woman, it's realistic, except that real people don't have so much snot running. But the Narm line was crossed when the characters were drawn drooling when they cry. That's sometimes too nasty to make the scene sad.
Usopp being accepted back into the crew is probably the worst crying scene. It really ruins the drama when Usopp and Luffy are both bawling like a bunch of five-year-olds.
The pirate Caribou had a mysterious Logia Devil Fruit that resembled mud. We learned the Japanese name for it is the Numa Numa Fruit. Probably easier to call it the Swamp Swamp Fruit
Some parts of the Viz translation of the manga drop into narm because of following some of the more questionable name choices from the 4Kids Cut-and-Paste Translation. For example, the Bird Bird Fruit and Dog Dog Fruit are called the "Tweet Tweet" and "Mutt Mutt" fruits, respectively. Not only does "Mutt Mutt" make no sense (the dog forms are very much exact breeds, not mixed "mutts"), it severely cheapens the Badass factor when both of Alabasta's guardian "spirits" proudly declare that they've eaten these ridiculous-sounding fruits.
Plus, Viz's refusal to use breezy language removes the drama from some scenes.
*Zoro gets cut by Mihawk*
Luffy: DARN YOU!
The Finnish translation of the manga sees your "Tweet Tweet" and "Mutt Mutt", and raises you "Kisukisu-marja" (roughly, "Kitty Kitty Fruit"). Yeah, that's the official name for the Leopard fruit eaten by Rob Lucci, one of the most vicious characters in the series. Made especially baffling because they could just as easily have gone with plain old "kissa", which simply means cat.
The scanlations. It may be a common complaint among scanlations, but it's hard to take a chapter seriously when the translator honestly thinks it would be a good idea to pepper the dialogue with "OMG"s and "WTF"s.
Let's talk about Vivi for a moment. For a while after she's introduced, she's referred to as Bebe, BB, and a few other names almost interchangeably before settling on Vivi. The Narm comes when they introduce Pell and, after calling him this for a while, suddenly start to refer to him as Bere when the panel in question features Vivi. This quickly ruins the mood of Pell's heroic sacrifice a few pages later.
As of chapter 574, someone has apparently finally broken the famed "no main character dies in One Piece". That person was Luffy's (adoptive) brother Ace... and what face does Luffy make to convey this tragic loss? A passed out Pac-Man. (Warning: spoileriffic link!) Not exactly the death of the Going Merry.
The death of the Going Merry itself was this for some. The fact that the ship starts talking as it's given a viking funeral, complete with the standard Inelegant Blubbering from almost everyone and Luffy and his ship trading apologies, may wind up ruining any tension built up over the course of the entire arc.
Kaku. Just Kaku. Between his Devil Fruit, his use of outdated slang, and his English dub voice, YMMV if Funimation's dub of Water Seven/Enies Lobby will be taken seriously or not. However, for the vast majority of the intended audience, he is a successful instance of Narm Charm, and at times the most popular villain or former villain in the entire series.
Film Z has Luffy effectively going to war with the title character's forces. The awesome is spoiled somewhat by Luffy wearing a a giantic chicken drumstick on his back.
An odd example occurs in the dub of the Loguetown arc, Luffy is about to be executed and his tone of voice as he tells his friends they're too late to save him kind of takes away from the drama the scene is trying to convey. His next line completely takes the wind out of the sails with him laughing and declaring "I'm still alive, that's nice". Needless to say Luffy is a master of Narm.