A mouth-mounted bone-induction MP3 player from Aisen Caro Chacin:
Once I saw those toothbrushes that play preloaded music clips, I knew we were getting close. the controls are a nice touch, though a Bluetooth remote would also be appropriate.
I'd prefer to control it by clicking my teeth, sort of like the iphone earbuds work - single click is a pause/play, double click is fast forward.
Anything that stops teenagers broadcasting their music at everyone in public gets my vote.