We all have characters that we hate. Completely, totally, despise with all our passion.
But is there any character that you completely hate, but then love at the same time? I think everyone can think of one. That antagonist in a book or movie that plays a major role in the MC's life. They come back, over and over, maybe they are the 2nd MC, or maybe just a side character with a major role.
In any case, it's characters like these that keep the story going. Sure, you may love the MC and any other supporting character, the book/movie might be just fine without someone with major attitude, but that one that you completely despise completes the story.
I love writing characters like these, don't you? There are several antagonists I've written about, that I absolutely love to hate. They all play a certain role too. They are there to create some kind of havoc. From the typical bad guy persona to a more secretive scheme... heh!
There are also MC's that you start out hating, then you love them at the end. Those types of characters are a lot of fun!