Chopper's first-person pronoun is おれ — the same casual, boyish "I" Luffy and Zoro use — and that's a small rebellion in itself. He is, on paper, the crew's physician: the one member with a formal professional title, 船医 (senni, "ship's doctor"), stitched into how the others introduce him. A character built for that role could easily default to polite です／ます speech, the way a real doctor addressing patients would. Chopper never does. He talks like the animal-turned-boy he actually is, not the credential he's earned, and the gap between the two is the whole joke: Franky can call him ドクター ("Doctor") post–Thriller Bark and get answered in the same rough register he'd use insulting a rival.

That rough register shows up most in sentence endings that drop vowels the way a tough kid would: not 嬉しくない (ureshikunai, "[I'm] not happy," the plain grammatical negative) but 嬉しくねェ (ureshikunē) — the え contracted and roughened, the mark of dialect-flavored bravado rather than careful speech. だぞ and だぜ close off his declarations with the same swagger: 海賊になるんだ！！ ("I'm gonna become a pirate!!"), not the softer になります a nervous kid might reach for. It's borrowed confidence — Chopper spent his whole childhood being told by both reindeer and humans that he didn't belong to either group, called 化け物 (bakemono, "monster") by both sides before Hiluluk took him in. The blunt endings are armor plating over that history, and they crack exactly when the history surfaces directly: 泣くかァ！！！ ("AS IF I'M CRYING!!!", Vol. 16, p.123) is the same denial reflex aimed at his own tears rather than someone else's compliment.

The compliment-denial version of that reflex is the character-defining bit, and the corpus shows it isn't a one-off: it's a running gag Oda restages at least four times across tens of thousands of pages. Drum Island supplies the template — Nami and Sanji praise his medical talent and animal-speech ability, and he detonates: バ．．．バカヤロ！そんなのほめられても嬉しくねェよ！！コノヤローが ("S-STUPID! ...it doesn't make me happy at all!! You jerk—", Vol. 17, p.176) — while the art has him dancing with joy in the same panel. The exact shape recurs practically unchanged: Franky calling him "Dr. Chopper" post–Thriller Bark gets ドルドドドクターなんて言われても嬉しくねーぞコノヤロー！ (Vol. 34, p.103); Camie praising his Heavy Point fighting at Sabaody gets そ．．．そんな嬉しくねーぞコノヤロー♡ (Vol. 51, p.130), complete with a heart mark undercutting the denial in print; Sanji's offhand "that was pretty impressive" on Fish-Man Island gets the near-identical そ！！そんな事言われても嬉しくねーぞコノヤロー♡ (Vol. 63, p.11). Same vocabulary (嬉しくねー, コノヤロー), same beat, four different arcs, a decade of story apart — this is Oda writing a tic, not a scene.

VIZ's translators generally chase the energy over the literal grammar, and mostly it works. 嬉しくねェよ becomes "IT DOESN'T MAKE ME HAPPY AT ALL," faithful enough, but the signature line stretches further: "S-STUPID! I'M COMPLETELY IMMUNE TO YOUR FLATTERY!!" turns a simple negation ("that doesn't make me happy") into a boast about invulnerability ("I'm immune") that the Japanese never actually claims — Chopper isn't asserting resistance to flattery, he's just denying, badly, that it worked. The English adds a swagger the Japanese undercuts by having him stammer the first word: バ．．．バカヤロ, the stutter alone telling the reader he's flustered before he's said anything. コノヤロー itself — literally something closer to "you bastard/this jerk," a rough deictic insult — drifts across renderings from "YOU SILLY..." to a flat "FOOL!!" to being dropped outright, which is defensible panel-by-panel but loses the one word that ties all four instances of the gag together as the same gag.

The line that breaks the pattern rather than repeating it is worth reading against it: 聞いてよドクトリーヌ！！おれ海賊になるんだ！！船医としてあいつらの仲間になって．．．世界を旅するんだ！！ ("Listen, Doctorine!! I'm gonna become a pirate!! I'll join them as their ship's doctor... and travel the world!!", Vol. 17, p.150) has no denial in it at all — no バカヤロ, no コノヤロー, just おれ stated flat and forward, the same pronoun he uses to reject compliments now used to claim a future. It's the vow that makes sense of everything else on this page: he learned to be a doctor from Hiluluk, the quack who died refusing payment from patients he couldn't save, and the boy who can't accept a kind word without flinching is, underneath the flinch, still trying to earn one. Read the anchor scene's other side on the Nami and Sanji quote pages — the two co-teasers who spend half the Grand Line finding new ways to compliment him just to watch him detonate.