I am curious where do you live? I also stutter on my name almost every time, and while every once in a while I get a bad reaction, it’s super rare here in Canada! If I had that multiple times a week I would be very pissed too lol. So I get that!  But also, from my experience, simply saying “yeah, I have a stutter, it’s a speech disorder” is more than enough to make people feel terrible and apologize, while also make you seem like a bigger person haha. So maybe you can try that? At least for me, it still brings me plenty of satisfaction and gives the power back to me. That might also keep the door open for you approaching them later and asking why they reacted that way. It sucks that it’s up to us to educate people about this shit, but the world isn’t fare in any way, so this is no different lol. We all just need to figure out how to live with this.