When you are inebriated or otherwise impaired, and it would be best to keep your sunglasses on because of intensely red eyes.
*Ashley* "Hey Greg, are you having fun?"
*Greg* "Ashley... shades down."
Order given by leader of a group when walking out of a dark area, such as an office building, mall, airport terminal, or theater into bright sunlight. Max style points are achieved when the posse lowers their shades in unison, like a precision drill team. For this reason, the group leader says "Shades" as a preparatory and after a slight pause for each member to reach up with their right hand to grasp their sunglasses at the hinge point, or to say "Wait! I'm fishing for my keys!" emphasizes "DOWN." The leader must also anticipate arriving at the exit and time his order appropriately.
Keith, Dan, and Jeff are easily approaching the exit with their shades propped coolly upon their heads. Seeing the bright sunlight outside through the doors...
Keith: "Shades DOWN!"