When you're walking along wearing headphones, you're sending two messages: One, "I don't want to hear you," and two, "I don't want you to hear what I'm listening to." They combine to a message of, "I'm in my own little zone over here, so don't bother me." Intentional? Not always. But that's the message I get.
So here is my question. If a headphones-wearer doesn't want you to hear what they're listening to, why do they have the volume so high that you can hear their music from ten feet away?
When I hear someone's headphone-music from ten feet away, this is the message I get: "I don't want to interact with you or anyone else in the world, and I'm pretending to try not to disturb anyone when I really don't care if I do, and I don't mind if I lose my hearing." Those poor, battered little eardrums. Personally, I'm somewhat paranoid about abusing my eardrums. My eyesight is bad enough that I don't want to damage my sense of hearing any more than I have to.
Headphones in general give off a vibe of disconnectedness with the physical world, which extends to things like cell phones and Bluetooth earpieces. They all say that, yeah, sure, their user is here right now, but that is so not the priority. The person using the headphones, cell phone, or Bluetooth earpiece is typically far less aware of their surroundings than they would be if they weren't using those things, which is something not-so-well-intentioned people can take advantage of. My sister once referred to the earbuds that come with iPods as those "mug-me white wires sticking out of your ears." And it's true--headphones in general are a sort of invitation for muggers, and the more noticeable they are, the louder the invitation.
Probably not the message the wearer intends to send, is it?