Labels are tools of convenience. It is understandable why we use them. Unfortunately, the objects of labels are not always immutable. If I call a hammer a hammer, it will be a hammer next week or even five years from now, but f I call someone a fool or a jerk, I may blind myself from seeing that person's wise or decent behavior.
There are, of course, people who so consistently demonstrate a certain quality that the label makes sense. Any behavior to the contrary is a rare aberration. Why waste time searching for it? There are two points of caution for the workplace:
1. If the person deserves the full-time version of a negative label, why is that individual still around?
2. If the person is a part-time practitioner, don't assume that the negative behavior is full-time. Sometimes the whiner or griper has a good point. Problems are not always surfaced by saints.