People who assume that your taste in music matches your mentality/behavior.
People who lump everyone's brain chemistry together as if we can all do that 1 thing they can do that helps them with that particular problem. Not all of us can just decide to change emotions like a light switch.
I get it all the time. I listen to heavy metal, numetal, and in general angry sounding music.
I don't have a explanation as to why it calms me down. Just like I have no explanation as to why the color blue makes me upset. It's a calming color supposedly, but mine is red, black, and gold. My sister's is green, purple, and red. I've just learned to not assume someone reacts the same way to external stimuli. Going to a special education school my whole life has shown me many types of people and their reactions to things. Mental health sucks, but learning what helps you is all that matters.
I guess both of those pet peeves are really just 1 in the end. People who assume they know how someone else is and feels based on personal belief's and not actually asking them and caring how they feel.