Things I hate: Waterstones. Mostly because of it's monopoly over physical books. Here in the UK, it's pretty much the only major bookshop chain, unless you count bargain books, which pretty much only sells dry history texts, arts and crafts, and childrens/teen books. But that's the thing isn't it? Why has waterstones become the leader of this market? Because they're the only reliable place for this stuff. WH smith's selection just isn't wide enough, and most independent stores are run by little old ladies who only stock older novels, and even then, little in the ways of sci fi, horror, and fantasy. Waterstones reliably offers a pretty good selection, and if there's a particularly popular book, you can practically guarantee they have it in stock.
Hell, the other reason waterstones annoys me is that they seem to take the view that books should rarely ever be discounted, and certainly shouldn't go down in price over time like anything else. And why do they do that? Simply because there's nobody left to properly compete with in their field, can't really blame them for reaping the rewards of their success.