Spoiler for like, any book existing.
I think mine has to be the villain in Mirror Man. Idk, he wasn’t intimidating, he wasn’t interesting. He was meh.
Also the villains from The Chain. Dear God they weren’t sympathetic in the slightest. The book tries to act like they were atleast pitiful but FROM THEIR INCEPTION, they were just evil assholes who enjoyed causing pain. The book itself wasn’t all that great anyways.
I’d say Straff and Sadeas are on different planes of evil. The kind of power grabbing and short sided evil Sadeas is very common. Straff on the other hand is a massive sadist who enjoys torment and torture for its own sake. For all that he’s a snake Sadeas never really does anything out of pure malice, it’s just good politics in his head.