Serial Bullying is often difficult to differentiate from Borderline Personality Disorder, and, in fact, some of the characteristics above fit more with BPD than with your average bully.

Bullies tend to "bully" for an audience--they rely on the passive approval of the "uninvolved" witnesses, as described above. They tend to do it to enhance their social position--the Borderline Personality Disorder individual reacts to perceived threats--often, the victims, are competent, socially adept, attractive, and relatively normal, rather than the sort of vulnerable outsider that the regular bully will target. As mentioned above, the BPD often torments secretly--