In addition to a couple of excellent answers, I'm going to say designer clothing.
I love magazine ads where a model is wearing a plain T-shirt that "only" costs $250, or jeans that cost $500. I lose my mind paying $45 for Levi's on sale; you'd have to be on crack to buy jeans for $500. Not even if I was a billionaire.
I grant you that some stuff that I buy that is on the expensive side is actually worth it. UnderArmour hi-tech fabrics really do work, and they are worth the money to me, not because of the brand name, but because of the function. But I buy generic versions when I can.