When you can sue your boss
The workplace can be a difficult and unfair space to navigate. Bosses and supervisors can be petty, dismissive and inequitable in their treatment of employees. Worse yet, they can single out a particular employee for particularly harsh treatment or some other form of discrimination. If you are that employee it's natural to consider bringing a lawsuit--you want to be treated equally and like your co workers are treated. Worse yet, a supervisor may be gunning to get you outright fired.
Washington is a "right to work" state which essentially means that your company can terminate your employment at any time for just about any reason or no reason at all. What your employer cannot do is fire you or treat you differently for an illegal reason. An illegal reason is one that involves discrimination. Discrimination typically--but not exclusively--involves a "protected class" which is the race/creed/gender/age/disability categories we hear so much about. There are multiple categories and they include exercising a legal right such as filing for workers compensation. Union activity is also protected.
In a legal case typically the hurdle is connecting the discriminatory treatment with being a member of one of the protected classes. What is not covered under Washington law is if your boss is simply unreasonable or speaks to you harshly. If you are considering taking legal action against your company make sure and document how the inequitable treatment is related to race, gender, religion, sexual orientation, age (over 40) disability, etc. This will give you a viable way to hold your company accountable.