Some of the injuries that I remember most have already been mentioned, but I'll go ahead and list a few out anyway.
Luffy punching Don Kreig in the face through his cape to this day makes me cringe. Also, when Luffy is pulling out the dart from his leg and it makes that noise…ewww.
Luffy scaling that mountain in Drum bare handed, always, always, makes my fingers hurt just to watch. The worst part was when he loses some altitude and his bloody fingers get all kinds of tore up digging into the side of the mountain.
When Luffy got impaled by Crocodile the first time, I audibly gasped because I was so shocked. I was like, "holy shit!" Also, every time that he got super-dehydrated from Crocodile's touch made me wince because I can't imagine how somehting like that wouldn't hurt like a bitch.
Zoro. Just…Zoro. I don't think that an arc goes by without me cringing at something because of Zoro.
Nami repeatedly stabbing herself in the arm with a dagger while screaming "ARLONG!" is her stand out, cringe-fest moment for me. The combination of her extreme emotional trauma and the pain of her self-mutilation easily rivals any of the injuries that the boys have taken in their fights, I think.
Usopp's face + Mr. 4's four ton bat = me cringing, a lot. The visuals of his busted up nose and the cracking sound that Mr. 4's bat made as it impacted his face are like, whoah. And then there was that whole X-ray effect for his skull, which makes it infinitely worse. In total, it is PAIN.
That scene where Sanji is fighting Gin and his internal injuries start acting up is just awful in the anime. He's all cracking and popping like some kind of freak thing, and it lasts for a while. The sound effects really make that scene extra-horrible.
Sanji's chest caving in from the pressure during his fight with Kuroobi was another scene that was infinitely worse in the anime than in the manga. The close up plus the sound effect was way ewww.
Sanji getting kicked in the nuts by Califa isn't really something that makes me cringe or anything, but he sure as smeg has my sympathy for what had to have been one of his most painful and humiliating moments.
Chopper all busted up after getting the poisonous mushroom for Dr. Hililuk was an image that really stuck with me. Even his antler was broken, and his leg was all sorts of mangled. It was like looking at a teddy bear that had been mauled by jackals or something; just horrible. By comparison, the mauling he got from Kumadori seemed rather mild.
I can't really think of any moments that made me cringe for Robin, other than what Impel Down mentioned about her biting into the Bridge of Hesitation and holding on with her teeth. Oh, and all of the pimp vs. ho treatment that she was getting from Spandam as well, what with all of the bitch-slapping and hair dragging. Ouch.
Minor characters, yay! Zeff cutting off his own leg with a rock and eating it in the manga was a serious "WTFingF?!" moment for me. That was a one two punch combo of self-mutilation and autocannibalism, and it was permanent on top of that. Tashigi's busted up leg from Robin looked like it hurt something fierce. Bellamy getting a Gomu Gomu fist to the head just had to hurt like whoah. Sodom and Gomorrah getting taken down in Enies Lobby really sounded painful to me. Gen-san's scars are crazy; the guy's like a roadmap and that's messed. Arlong getting his nose bent in half, even though he's an evil bastard, made me wince in sympathy.
EDIT: How could I forget the dude pictured in the first post of this thread? That's some crazy Vash the Stampede level body scarrage there. Talk about super grim.
Sheesh, everyone here can not stomach violent scenes. There really is not anything really violent and stomach turning about One Piece. If you really want to watch a violent anime, go watch Elfen Lied.
You want violent and gory? Go watch Cannibal Ferox or something. No, seriously.
And for the record, just because I find some scenes in One Piece to be violent or cringe-worthy does not mean that I can't stomach them. I've stomached watching a child getting vivisected in graphic detail (actually he was being disected, but in the film it was vivisection), and really there isn't anything in any anime that can even try to begin to compare to that. But that doesn't mean that there aren't scenes in One Piece that don't leave me cringing and wincing or just going "jeezus", even though they're not as bad as some other stuff out there.
~ jj ~