Black Noir. I joked about using his face as an emoji, but seriously, his face really does get grating, and in a world of already repellant and wicked abominations, he stands out as utterly odious and despicable.

(Dis)honourable mentions include Mark Tomaso, William Carver, and Shou Tucker.

Umbridge. Not only is she evil, but she is annoying also. If your villain is hateable for how evil she/he is and also because they are annoying, you created the ultimate hate sink

Alan Yates because he has no humor, no redeeming qualities (obviously) and is absolutely psychopathic.