Breakin' out can be used as a verb or adjective. In its verb form, it means partying hard. In its adjective form, it means a rowdy or good time.
> Q: What did you do Saturday night?
> A: We hung out with some friends at Jim's house. We were breakin' out.
> Q: Did you go to that party Saturday night?
> A: Yeah. It was breakin' out.