Creating "bad" characters, and relating to them

Lately I've been fascinated by the idea of writing a story with a very unlikeable main character. Author Gillian Flynn is a pro at this, in her books Gone Girl, Dark Places, and Sharp Objects (creepy, horrifically disturbing books, but nonetheless interesting because they are different from what I normally read).

But "unlikeable" doesn't necessarily mean unable to relate to. I don't like villains that are evil just for evil's sake. The best "bad characters" are multidimensional. They have history. They also have a handful of good qualities.

While working on my book of poems, I can't shake this idea that keeps coming back to me, usually when I'm trying to sleep. It was originally going to be a redemption story about a pastor who is a saint to his community, but has a terrible secret. Now I may be shifting my focus toward a teenage girl, who may or may not be related to him in some way, but is known at school for being a not-so-nice person. She may be the type to use bullying as a way to build up her own confidence. She'll do this because she herself is weak, even if her victims don't see that.

I believe in this idea because I don't believe in truly "good" people. I don't even think of myself as a "good person" (though in retrospect, I'm hesitant to call myself a "bad person." Most people wouldn't say that about themselves, would they?).

I think about my personal prejudices...feeling disdain for large families with loud children coming in to coffee shops while I'm studying, letting their kids run all over the place and try to talk to me while I'm taking a timed online quiz (yeah, that happened once).

Mass-generalizing people who can't put sentences together and use the proper forms of "your/you're" as stupid, even if it's a proven fact that our education system doesn't adequately prepare students for the business world, and "business skills" may include proficiency in written communication.

Having a those people mindset regarding those who grew up in one place, in one culture, for most of their lives, and have had little interaction with people who are different from them. Never mind that I too can be one of those people. I am embarrassed by this fact.

So what makes a character truly unlikeable? What distinguishes an average person from the Hitlers and Mother Theresas of this world? In one last gesture of good faith, I'd argue that many people are simply not aware of how "bad" they can be. My goal then, if I choose to write this next story, is to develop a character who is aware of her personal badness, and has no desire to change.

At least, not yet.