With my primary workload having been with internet productions, I can sure as hell tell you the traits of a bad director. Guys who don't feel bad about taking frequent breaks, freak out when challenged by something or someone, lose their cool on making a decision/solving a problem (and I always end up being the one to bail them out), and never forget the wonderful "I'm the director!" when they don't have a good explanation to a choice affecting others working on the project.
Now that I think about it I don't think I've ever worked under a great director.