There were little white wires hanging down from their ears, or tucked into pockets, purses or jackets. The eyes were a little vacant. Each was in his or her own musical world, walking to their soundtrack, stars in their own music video, almost oblivious to the world around them. These are the iPod people.
Even without the white wires you can tell who they are. They walk down the street in their own MP3 cocoon, bumping into others, deaf to small social cues, shutting out anyone not in their bubble.
"The eyes were a little vacant."
GOT damn the pusherman!
(same result, smack or wires)
I have returned to college and see it all the time there - it's a little annoying. Your use of the word coccoon is very appropriate.