I believe by most hated, she means most hated by the writers, who put him through so much.
I think they wanted an O'Brien, a man to roll in the mud and poop so as to show the universe is not a nice place, or something like that.
And considering this thread is in the SPOILERS section, I think putting spoiler tags is a bit mute. If it wasn't originally, I still side with the OP.