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.
Fwi-Song from Consider Phlebas. https://theculture.fandom.com/wiki/Fwi-Song
Not the main villain in the book but extremely despicable nonetheless. Punching above his weight, if you will.