If you're the person who is easily annoyed with the chewing sound of your brother, repeating clicking sounds of your seatmate's pen, or the breathing of your fat friend, you might have a condition of a disorder called misophonia. Those triggering noises give a flight-or-fight response like you want to walk away from them or grab a gun to kill that nuisance. In fact, misophonic people cannot control their emotions that allow their brain to consider those simple sounds intensely irritating. It might even increase their heart rate and sweat more.
Inside the brain of those people, scientists found abnormal connections between the frontal-lobe area and the anterior insular cortex (AIC), a grey matter but buried in a deep fold at the brain's side, and are responsible for processing emotions and integrating signals both from the body and outside world. So undoubtedly, their reactions are aggressive towards those triggering sounds.
But good thing headphones or earplugs were invented. People with misophonia can use that to help them calm down and stop them from committing a murder.