Dancepants is a conceptual MP3 player that seems like a straight-up cruel product. Basically, its a music player that only works while you're running. If you stop, the music stops. If you cramp up or feel sick, you've just gotta push through it.
You don't have the willpower or self-control to have power over your own music! You're so weak that you need to be punished for stopping your exercise, no matter what!
The one good side to the product is that it's charged up by your motions, so there's no batter to recharge. At least in theory. I mean, this product doesn't actually exist, so who knows if that would really work.