Ooh, constantly. One of my antagonists is so needlessly cruel and manipulative that I'm ashamed of him. Every time he adds one more miserably mean thing to the heap of crimes he's committed, it makes me all the more glad that I can mete out a suitable punishment for him in the distant future.
A few other characters have habits that I'm not terribly fond of, but it makes them more real, so I left them in the story. They make choices I wouldn't, have preferences I don't share, and pursue goals I would eschew. It helps with making each character unique and distinctive from one another, and not clones of the author.