Avoiding negativity about previous managers and your reason for leaving a company is important. Even if you have a boss from hell (i.e. The Devil Wears Prada), you should never admit it!!!! I would recommend such subtleties as: “the company is going in a direction that is not in-line with my career goals”, “there is no room for growth” or “I am looking for better prospects and a better work environment”. This is not to say that you should lie, be honest. Just avoid mentioning the bad stuff.
Meryl Streep as the "boss from hell", Miranda Priestly in The Devil Wears Prada