If the job is open seven days a week, don't complain if you have to work each of those days.
It's illegal to force people to work 7 days a week. (The fact that small business owners of various kinds do that voluntarily not withstanding).
That's fine but they established an a precedent when they allowed him off previously. Fire me fine, but don't object when I catch you at the local bar and bust your head for you. Of course that's my personal view of dealing with sh*thead supervsiors.