Does the sound of someone chomping on a piece of gum set you off, or is it one of those easily ignored background noises? Scientists use the term misophonia to describe what's happening to people in the first group. These people tend to get annoyed by repetitive noises (chewing, breathing, or typing), and this video from SciShow gives two plausible explanations. Unfortunately there isn't a quick fix, aside from buying earplugs or telling the loud chewers around you to eat somewhere else.
Does the Sound of Chewing Piss You Off? Here's Why