OOOh, trick question again. Remember we don't want to bash former employers. The interviewer knows if you talk bad about someone to her, then you may talk bad about her one day.

So how do we handle this one?

You could say, "I've never had a really bad boss, but I have learned some things NOT to do." This way you are not directly pointing the finger while still acknowledging you are aware not everyone is a good manager.