AITA for storming off from my sister’s wedding after she deadnamed my son?

Picture a wedding buzzing with perfection—crisp shirts, flowing sundresses—until my sister (38F) trips over my son’s truth. I’m 45M, solo dad to three boys: Andrew (17), Connor (15, trans), and Max (14). Connor’s been out five years, socially transitioned for two. My sister’s “indifferent” to it, but her wedding? A battleground.

She demanded “Nia’s” dress, balked at his tie, and slapped his deadname on a card. I warned her: respect him or we’re gone. She sneered, “Not at MY wedding.” I called her a bigot, we bolted—family says I wrecked it. AITA?

This wasn’t about her big day—it’s about my son’s dignity. Connor’s trans journey’s no secret; my sister’s “Nia” jab was a deliberate shove. Dr. Diane Ehrensaft, a gender expert, says, “Deadnaming wounds—it denies who they are” (from The Gender Creative Child). I gave her a heads-up—shirt and tie or bust—she agreed, then flipped. That card wasn’t a slip; it was defiance. Her “any other day” line? Pure dismissal.

The fallout? Her control clashed with my duty—70% of trans teens face family rejection (Trevor Project, 2023), and I won’t let Connor join them. I could’ve stayed quiet, but silence betrays him. She escalated; I exited. Next? Low contact—she’s unbent, I’m unbowed. Readers, am I the ass for bailing, or her for bigoting?

Reddit’s roaring: I’m not the asshole. They’re all in—praising my dad game, torching her transphobia. “Nia any other day” gets no pass; it’s a slap, not a stance. They say I’m a rock—some suggest petty revenge (hello, “Miss Smith”), others a clean cut. Consensus? I’m golden, she’s the scene-stealer—in the worst way.

So, AITA? I stormed out, tie intact, kids in tow—her wedding’s shadow doesn’t dim my son’s light. Maybe I could’ve whispered, not roared, but “Nia” on that card was a gauntlet. Grief’s no excuse—she chose disrespect. If your kin deadnamed your kid at their gala, would you sit pretty or split? Drop your take—let’s tie this up!