Don't bad-mouth your previous employer, but you can put things diplomatically. For example you can say "it was a very challenging work environment" instead of "my boss sucked."

Also be prepared to talk about everything you learned and what you could have done better yourself. It seems like you have a good idea with hindsight about a lot of things that didn't seem right at the time.

But as noted by others, employers understand that there are toxic work environments out there. Be honest but don't belabor the point.