How should he react?
Well, for the starters…
He should react sanely. Like a human. Politely.
Served non-vegetarian food, is that the end of the world?
So what he has non-vegetarian food in front?
If he doesn't like it, he must politely refuse and ask for the food to be replaced with something veg.
(Courtesy: The News Minute)
Even if his request cannot be fulfilled, he must still be polite and empathetic. Either leave the place and go somewhere where they serve vegetarian food. Or, if he can’t leave (for example: he's on the flight), stay hungry.
Even if the person has served you non-vegetarian food purposely, knowing well that you’re vegetarian, he must still remain polite.
Even if he is overly religious about these things, he must still remain calmed and polite.
It's just food for Christ sake.
Remember, you don’t need reasons to be good. Or, for that matter, being good to others is never a bad thing.
There's no reason - literally NO reason - to be anything but polite when you're vegetarian but are served non-vegetarian food.
Be nice to people.
No matter what, always be nice to people.
Stop being cynic. Stop complaining. If you don’t like what you’re getting, look for what you want somewhere else. All the while, be polite… even when the person in front of you is being *insert expletive here* to you.
Stop minding small things.
Spread joy. The world needs it.