Lucky Star. The only reason I say this is because I cannot think of any anime I hate more. That sounds bad, but it's true. There aren't any others I hate more. People talk a lot about Lucky Star. I finally watch the darn thing. It sucks, I can't sit and watch it. And not because it's "girly" or whatevers, because I watch a bit of relationship centered anime, but it never appealed to me. And yes, I watched past the first episode, because a lot of people say when you try out a show, watch the first 3 episodes or so, then complain. So I did! I don't see the big deal in it, in fact, I bet most of the fans are the dudes who this show's characters appeal to. It makes a buttload of anime/manga references, but I personally didn't find it interesting enough to keep watching it.
I originally hated Excel Saga until I realized the true nature of the show. But I cannot watch Lucky Star. I do not understand its popularity, like I don't understand MLP:FIM's popularity.