I can't stand others eating an apple, but I can eat one without and issues. The same behavior holds true for playing with loose coins or cellophane wrappers.
How do you react to eating an apple yourself?
How do you react to eating an apple yourself?
Also, I don't think it's cultural and I suspect it might be hereditary.
Even if I finish first and the other are still eating, it's really only when I didn't eat / not eating that it infuriate me.