pathological lying
there hasn't been done a lot of research on this mental disorder yet, but it seems everybody knows at least one person who is a pathological liar, i.e. someone who lies and believes their own lies. there are known diagnostic criteria for »antisocial personality disorder« and often the chemical imbalance that causes the illness can be treated similar to borderline syndrom. however, it is very complicated to convince the patient of his infliction since the lying in itself is the perfect defense mechanism, a bit of a catch 22.