1.)Something you tell someone who is tring too hard to be "hip, and with it" in a materialistic way.
2.) a way to tell someone that they are freaking out unnecisarily; kind of like chill out, but more cool
3.) a dance and song from the movie Labyrinth
1.) Dude, chilly down, no one gives a rat's ass that you have a hummer.
2.)Hey, you're being a douche bag, just chilly down.
3.)"Strut your nasty stuff, wiggle in the middle, get your town talkin'. Bad Gang. Chilly down with the wild gang."
Means to chill with. From Labyrinth
(1986) and most of Coastal US.
Chilly Down with Fire Gang.