Goodness, I have the exact opposite problem. I always try to be "realistic" onstage, but sometimes it turns out to be really melodramatic and somber and... bad. I always focus on the drama and forget to have fun with my character.
My advice is, don't focus too much on what makes YOU angry. Think a lot about your character: What is it that makes your character so "evil" and "despicable"? Why do you think your character has chosen this path of life? What makes your CHARACTER angry and mad? Is there a lot of angst? Buried issues? A tragic backstory? A naturally cynical and irate personality? Be specific. Talk to your director about the direction he or she may want for your character, and don't be afraid to contribute your ideas.
Good luck, and I hope this advice helped!! I had the same trouble when I had to cry onstage, and I kept concentrating on what made ME cry instead of my poor character. Keep working! Never quit!
By the way, what role is it? As a natural fan of "somber theatre" I'm always looking for a lovely villian to ponder.
"The art of Illusion is the art of love; and the art of love is the blood-red heart of the world." - Tony Kushner, "The Illusion"