That sound is not the only one that triggers my response, but I chose it because of this argument: I don't think anyone would argue that there is something culturally wrong (at least in western culture) with eating apples around other people. And there isn't really a way to eat a whole apple without making a sound that makes me irrationally furious.
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.
That's right - I don't feel anything when I am eating myself, or even when I am at a lunch table with others munching with me. It's only when I am not the one eating. I also get irritated when I am on the phone and the person at the other end is chewing or lapping.
Also, I don't think it's cultural and I suspect it might be hereditary.
Interesting. What if you listen to a recording of yourself eating? While you're at if see how much you can distort it before it stops or starts to bother you. E.g. Played backwards, at double speed, half speed, etc.