In one word, professionally.
If you have ever felt the growing urge to let management know just how you feel, you should know that the courts care about how you do it.
Daniel Lublin uses three examples to illustrate the hazards of “talking smack” about your boss:

• Following a confrontation with her boss, Maria Van Der Meij wrote a letter to the board of directors calling her manager cowardly and unethical;
• Yingyi Chen wrote a letter to shareholders addressing his dissatisfaction with management;
• Dawn Marie Bennett wrote a letter to her boss listing complaints of negligence, disorganization and incompetence.

The courts upheld the dismissal of the first two, but not the third.  Why? Employees are entitled to criticize management without fear of reprisal; that being said, a harmfully intended public expression differs from a privately reported grievance.
Lublin offers the following advice to irate employees: “the manner and tone in which they express them (complaints) must always remain professional. When such criticism goes over the edge, an employer is not required to tolerate it.”