Sometimes, a supervisor just doesn't get along with one of his employees. While the employee may think the reason has something to do with a protected characteristic (race, age, sex, etc.), that may not be the case.
When HR receives such a complaint, it obviously must investigate. But if you find out that it's really a case of clashing personalities (not discrimination) you can close the investigation --perhaps with a warning to the supervisor to check her attitude.
Recent case: Tham, who is of Vietnamese origin, complained that her supervisor, who is Bosnian, spoke to her harshly but was kinder to workers who spoke Bosnian. However, after investigating, HR concluded that ethnicity wasn't a factor in this dispute.
After Tham was fired for a series of workplace infractions, she sued, alleging a hostile work environment based on her national origin. She cited the supervisor's harsh tone as...