NTA. I have misophonia as well, and unfortunately one of the symptoms of misophonia is that noises enrage you. It's not just that they bother you, it's that they invoke a feeling of absolute rage, and that can be really hard to control in the moment.

OK, so, I also have ADHD so my impulse control is shit anyway. So I'll blow up sometimes. Sometimes my mother will eat around me, she has a jaw defect where she can't close her mouth when she eats and I will sometimes just go "can you not!" or "can you go away!"

Or whatever - but those things are shitty to do to another person. My misophonia, my problem. Not anyone else's especially for basic human conduct such as eating. I do my best to come up with alternate solutions.

(I discovered that turning the sink on masks the noise, so now I just turn the sink on when she eats downstairs - my misophonia, my problem, my solution, my responsibility, not hers). It's his autism, it's his responsibility, it's his problem.

If he's that bothered by nachos he should frankly have just stood up and left, I have done that millions of times around other people when little noises set me off. Screaming at people and expecting them to cater to your neurobehavioral deficits is not the way to encourage cooperation.

It just isn't, does it suck? Is it truly his fault that he has these issues? No. Is it fair? Nope. But that's life, and you have to work with people if you want them to cooperate with you and help you.