As per the OP's irritation with this school, I think it wouldn't hurt to express in your letter exactly why you are declining acceptance. It's too late to help you have a better experience but if qualified candidates start turning them down for being rude/arrogant, some of the less "customer friendly" admissions offices might start to come around to the competitive world that they live in. There's nothing inappriopriate in my mind about telling them what part of their process turned you off...