Ask HN: How do detect a crappy boss / toxic environment when interviewing?

I am currently working in a position that felt like a great startup to work at during my interview. However, a few months into the job I realized my boss was a complete and utter asshole. Given this is my first job out of college, I've stuck with it and I am looking for a new role. How can I detect during the interview / research phase to avoid such situations?

Some things I've been doing is looking at Glassdoor but the problem with that is the reviews are highly dependent on the role, or the department or some manager who may or may not still be at the company.

I am a pretty average developer which is why I was kind of desperate for that first job out of college but after getting more experience, I know I can do better than this.