Much like "sick" or "ill" unhealthy is the newest word used to express awe or approval of something. It can be applied to any noun but is often used in a sequence.
1. Dude that trick was unhealthy
2. Yo, this samwhich is mad ill unhealthy sick nasty
The opposite of health food. You go to a "green" market for health food, and you go to a burger joint for food that is guaranteed to raise your cholesterol level to the top of the Empire State Building and load you up with a week's worth of sodium.