Creating bad guys or gals for your story is usually easier and more interesting than creating good ones. It’s probably because they have built-in conflict, and conflict is what makes a story hum. One source of good material for wicked, evil characters is your own experience.
All of us have encountered people in our lives that have mistreated us, insulted us, or lied about us to others. When you think about them, old emotional wounds open, and thoughts of anger and even hatred flare. Use this bitterness.

Use this bitterness.
The best way to deal with emotions toward such people is forgiveness. Bitterness and revenge are self-destructive. There is an old saying that you should dig two graves if you go seeking revenge. That does not mean you cannot use your enemies, and the strong emotions they trigger, as a rich source of material for creating loathsome characters for your stories.
It can not only help you craft engaging, memorable villains but in a subtle way, you get a measure of payback without the cost of overt revenge by immortalizing the abhorrent character the antagonists in your life in a work of literature.