‘Lack of interpersonal skills’, ‘not a team player’, or ‘not enough of a people person’ are often reasons cited when you are denied a promotion. For any employee, they can be extremely frustrating statements. The criticism can sting personally and is vague about how you can improve.
Sometimes, it may be true that you need to develop your teamwork and team building skills. If your job requires special people-handling skills, then your employer would be right to promote people who are better equipped.
However, ‘not a people person’ can also be code for ‘the boss just doesn’t like you’. In such arbitrary favouritism, you may very well have legal options available to you.