Any advice on writing really hateable characters?

I've had this problem twice now where I have a character that's supposed to really get on the reader's nerves, but instead becomes to likable or cartoonishly evil. More often the latter. Any advice?

Edit: I'm not talking only villains. Actually none of the characters I mentioned ARE. But any advice is still very appreciated :)

Edit 2: I did NOT expect this much response. Thank you!