Today's Since You Asked advice column in Salon is about a woman who can't stand to hear other people eat. I'm the same way, though not as afflicted as the letter writer, in that I don't usually hear other people eating if I myself am eating. And it only started to bother me around late high school or college.
I don't think what I have is "hyperacusis" or any kind of medical condition. I don't really know why the sounds of people eating can make me so angry. It's not too bad with strangers, as long as they're not really loud eaters (I could never live in Asia, where the cultural norms allow louder eating, for this reason), but with people I am close to, especially people I live with for long periods of time, it gets really bad. And raging at people for chewing is not really an acceptable behavior.