The best boss I ever had kept their stress in check and never made me feel like I was going to be yelled at for making a mistake. They consistently gave me actionable tasks to improve my skills and minimize further mistakes in that area. Active listening was their default state of being. 

The worst boss I ever had started the relationship by telling me they only hired me because they had to, but they did not want me around, so I needed to stay out of their sight. They were consistently fluctuating in levels of anger and never gave feedback.