Yonemi Kamon from Battle Royale. The administrator of the Battle Royale Program, where high school students are forced to kill one another. Hobbies: watching students kill each other, killing students, joking about said students' deaths, raping orphanage directors, etc. Consider: when the teacher is killed in the movie, it's because the main character shoots him. In the novel, Shogo Kawada shoves a sharpened pencil against his throat, killing the teacher. In the manga, they shove sharpened pencils into his nostrils and slam his head against a desk. He earned it. Kamon is one of the most evil men ever depicted in manga.
What makes Yonemi so noteworthy (and awesome) as a villain is that unlike the movie portrayal of the Director, he doesn't even pretend to buy into that crap about maintaining order or protecting the honor of the Empire. He enjoys raping and killing, and he's a huge fan of the Program because he gets to see teenagers deal with gut-wrenching emotions before dying horribly. He's so hardcore, even soldiers are visibly nervous around him.
Kazushi Niida is a sexual sadist who fully embraces the chance to rape and kill his classmates. One of the first things he does is murder a classmate that was having a mental breakdown and afterwards he takes her weapon and says "Should'a at least fucked her first." Later on he propositions Takako Chigusa because "they're both going to die", showing that he knows his chances of survival aren't good but he's more interested in raping and killing and when she refuses he tries to rape her and smashes her face to a pulp in the process.
Toshinori Oda is a really scummy student with a superiority complex and eerie similarities to the Columbine shooters. It seems like the Program was pretty much designed for people like him, and he relishes the idea of slaughtering the classmates he loathes, especially girls.
Kazuo Kiriyama from The Film of the Book stands in contrast to his emotionless counterpart from the book and manga versions. Kiriyama in the film is a ruthless and psychopathic Blood Knight who voluntarily signed up for 'The Program' to be able to hunt down teenagers for for fun. Throughout the film, Kiriyama wracks up the highest kill count, not caring if his victims are helpless or not, and after gunning down one girl, he uses a megaphone so everyone around can hear her pain and his execution of her. While he never speaks a word, his Slasher Smile throughout the film speaks volumes for how much he is relishing his murder of everyone around him.