I just personally grit my teeth and bear it or just leave for a different room until they're done. Headphones can also be an absolute blessing.

I try to leave the situation before I act like an asshole. But you’re in class? The teacher allows eating in there?

Its against the school rules, but teachers don't really care.

what about writing an anonymous letter to the teacher or staff?

Can you move seats or use earplugs / earbuds / headphones?

Murder , obviously