Generally speaking, there is no law governing civility in the workplace. Courts and the legislature have seen the difficulty in getting involved in personal disputes at work. This seems counter-intuitive to some people, as the workplace is in some respects highly regulated. However, the laws that protect employees from certain kinds of harassment and mistreatment apply to specific important rights; for example, the right to be free from discrimination on the basis of race, age, gender, etc., or the right to speak out about matters of public importance. There is no right to be free from unkind or even unfair treatment. If that were the case, much taxpayer money would be spent paying judges to decide who was mean to whom on a certain day.
However, there is extreme behavior that may be so bad that it rises to the level of “intentional infliction of emotional distress.” That is, in some “extreme and outrageous” circumstances, courts find that the mistreatment constitutes an actionable personal injury for which the employer should be held liable. However, these cases are few and far between and courts tend to be suspicious of these complaints.