Maybe if you understand why people react like that, you can be more than just frustrated about it.
Most people know that it's morally questionable to eat meat, but they do it so often they'd have to consider themself evil to accept that. The alternative is to just double down on it and exclaim that the non-meat eater is the baddie for pushing their beliefs on people.
You can notice it when you just subtly bring it up and the way people overreact.