I thought Kirsten Dunst was cute and attractive for some time now. But now that you mention it, she can look quite ugly time to time. She gets that mousy piggy face. If you put 50 pounds on her, I think you get the sadistic concentration camp guard in the movie "Seven Beauties"
http://www.imdb.com/title/tt0075040/
One person I find particularly unattractive is Sarah Jessica Parker. I just don't get it. She is quite scary looking.
On the men's side, I just don't get what Colin Farrell is all about. His face is perfectly ordinary.