Next to a perceived lack of respect, it is clear from the myriad of posting across the web that the thing that most angers us about our managers is them showing favoritism.
Jobswill.com has a perfect illustration. Favoritism in the Workplace describes a tale of woe and favoritism in an organization where those who do not get along well with management, or who have not found favor with management, live in fear of making a mistake.
The anonymous poster describes a co-worker who made an "honest mistake" and was convinced he was going to be fired. Meanwhile, a female co-worker who "misses work constantly, dress inappropriately" and "talks trash about the powers-that-be," is allowed to get away with anything. Why? Because she is a favorite of upper-management at this company.
What is this contributor's advice for situations like this? Document everything that the favored employee does that would normally earn a reprimand, for use in court, should you be fired – although whether or not a lawyer would take up such a case, is open for debate.
But what all this highlights is that managers need to be careful about how they treat employees. Those nuances of behavior suggesting that employee A is preferred to employee B might not be as hidden as you think. As this anonymous writer asks, "why in the world do employees suck up to bad people? Why do they ride the good and kiss the bad?"