Characters: Who do you not love?

I'm taking a class this month from the Maryland Romance Writers about writing in depth characters. Lead by Linnea Sinclair, it's been a challenging course as I delve deeper into my main for The Conclave. Since I'm taking the villainous standpoint in my book, and telling the story as the villain (who is also the hero but never stops being a villain) I thought I would take a moment to ask you, my dear readers: What character have you read and hated. Why did you hate them? Was it because they were so well written you couldn't help it or because they weren't written well enough to let you enjoy them?