A fad that started with certain female celebrities who got black eyes from their husbands/boyfriends, but needed to make public appearances anyway. They aren't cute, or appealing in any way. Their only purpose is covering one's bruises and/or making oneself look like an uppity bitch by purposely hiding ones expressions behind a bitch-trendy facade.
Big sunglasses don't say "I'm better than you". They say "I think I'm better than you because he still loves me even if he does beat my ass every night after the show."