She was my first thought for this topic, mainly for her ending, but you're right the way she was written through several reasons was even worse. Really sad how she went slowly from most hilarious(or top three anyway) too lamest Buffyverse character, and I don't even know when exactly I stopped caring. It's of course always hard for the writers to deal with the hilarious over the top characters, because you can't just make the same jokes over and over again and you need some character development. I think Wesley is the example of when this worked best and Cordelia ... the opposite.