If there is one prerequisite to villainhood, it must be confidence. Confidence not inspired by ability, experience, or logic; confidence inspired simply by... itself. The confidence to say (out loud, of course):
"Garbed in this garish costume, I, Dr. Scheme, shall conquer the world using only easily broken instruments, followers with glass jaws and atrocious aim, and my expensively byzantine plans!"
Do you think Dr. Scheme has trouble asking for a raise or saying hello to that pretty face in the bar? I think not. And I'm sure he's got a ready ray-gun to fall back on, too!