Pre-owned Designer Cocktail Dresses: Theory Casual/Cocktail Dress, Size 8Because looking this good shouldn't be this easy but it is. This Theory black spaghetti strap dress is one of the most stunning pre owned designer cocktail dresses you will find absolutely gorgeous and impossibly glamorous. It still looks completely brand new. Theory is known for impeccably crafted, sophisticated designs that feel as luxurious as they look. This pre owned designer cocktail dress is a perfect example of the brand at its absolute best.