We're all villains already. We just need to find the person who sees us in that light. In their eyes, they would be the heroes, and we would be the villains. In our eyes, it would probably be the complete opposite. To describe myself if I were a villain would be the same thing as describing myself the way I am now, just with more focus on the negative parts of me. But I guess the point of this question was to play up the worst, most villainous traits in us to form a character more like the kind of villain we'd see in fiction, right?
If that's so, then I would be one who wants to prove a point. What the point is wouldn't really matter. Nothing will stop me from proving that point, no laws, no code of ethics or morals. It doesn't matter what cruel or inhumane means have to be taken to prove that point. It doesn't matter how much has to be sacrificed, let it be the lives of others or even my own. After all, those are just people. Just flesh, skin and bone. What I would be fighting for is an idea. And an idea is far more important than any human that has or will ever live.
As a side note, villain me would probably be that annoying kind of villain who talks to much and makes those cheesy, villain-monologue speech things. 'Cause, you know, I like to ramble.