I think mine would have to be a three-way tie.
1. Grand Marshal Garithos (Warcraft 3: The Frozen Throne). This guy was just the biggest, most arrogant, racist bastard I've ever seen in my entire history of gaming. First off, he disregards Kael'thas's warriors as an asset, despite their strong grasp of magic and that the high elves were the only real priests in the Alliance's army, to the point of giving them more and more suicide missions in the hopes they are all killed by the Undead. Second, in one of the missions in the Undead campaign, one of the side missions is to go rescue a contingent of dwarves, and he only berates them for getting lost. Finally, one of his "joke lines" is "The only good non-human is a dead non-human!" and another is "Never trust an elf!" He's a complete racist and I'm glad he's killed after that mission in the Undead campaign I mentioned and eaten by ghouls.
2. Tidus (Final Fantasy X). He's completely unlikeable and a royal idiot. Plus, what the ass is wrong with the way he looks?
3. Dane Vogel (Saints Row 2). Dane's the Head of Special Projects, really it's just a fancy name for big-shot for the Ultor Corporation. He's behind the renovation of the Saints Row district and stamping a great big Ultor logo on it, he's doing the same thing with the Suburbs district, and he's trying to get the permissions to do that same thing to the rest of Stillwater, starting with Shivington. And come on, what's wrong with a place named Shivington? It sounds like a real nice place! Plus, rumor has it he wants to tear down Tee'n'Ay (it's a strip club your character is a patron at)! That monster! In truth, he's just a corporate businessman who gets involved with most of the gangs in Stillwater, with the exception of the Sons of Samedi. He pays protection money to the Ronin because the Ultor corporation owns a casino in their territory (though those ties are eventually severed), he points the Saints in the direction of where the heads of the Ronin, Kazuo Akuji and his son Shogo, live, and the Brotherhood get him to use Ultor's lawyers to get them out of jail. Though admittedly, the leader of the Brotherhood, Maero, DID kind of have Dane in a chokehold about a hundred stories above the street and threaten to drop Dane if he didn't because he needed the extra manpower to fend off the Saints, but that's beside the point. Dane's a manipulator, and he can easily bend others to his will with his words, to the point of making Ultor look like the victims when their Pyramid, a research facility that makes weapons and body armor for the Ultor security team, is exposed. Eventually you do a story mission to kill him, and I couldn't help but savor every second of him being shot in the face.
