Worst bosses: Ditherers, or opaque and random ciphers. Never present. Jerk you from one task to another. Surprise you with bad reviews. Unwilling to pay for good tools ("What's wrong with Notepad?") Sees you as a fungible cog or chess piece to be moved around. Often non-technical, or "used to be technical" in an ossified region of the industry (e.g., large aerospace firm). Uses Scrum as a platform for micromanaging.
[I made a decision 25 years ago never to be a manager. I recently had the opportunity to try it out again for a summer, and it sucked just as hard as I remembered. I am an engineer, and I work with people in a far different way than good managers do.]