Brad, Angelina, Jessica Simpson, Posh, Jessica Biel, Paris Hilton and countless other celebs have been photographed sporting these shades.
And you can, too. They look great on everyone, guys and girls. They're trendy, but never go out of style. How many accessories can do that!
Rachel Zoe also says that sunnies are the universal "do not disturb sign," so unless you're on a plane and would rather sleep than chat with the stranger sitting next to you, remove your sunglasses when you're not outside.
To that point, unless you're outdoors, I think it's impolite to have a conversation when wearing sunglasses. You should be making eye contact.