One of the reasons you need to be diplomatic in dealing with a boss or coworker who is difficult is the lack of a single wrongful termination law. Basically, anyone who is employed on an "at-will" basis (which means there is no employment contract) can be terminated at anytime. Since most people are employed at will, employers can generally terminate them even without cause.
The only restrictions are those put in place by federal laws (the laws prohibiting discrimination, for example) and those in contracts (such as a collective bargaining agreement); ignoring these restrictions when firing someone would constitute so-called wrongful termination.
From a practical perspective, most employers wish to maintain good relationships between managers and employees, so there are provisions in place for handling whatever disputes and disagreements arise. Nonetheless, you should be cautious in bringing up complaints and be sure to follow any procedures your employer has established.