Once upon a time psychologists would diagnose someone as being a psychopath. Something very interesting happened though - the term exploded into the popular media with novelists and moviemakers all using the term as a label for a complete nutcase who's not the sort of person you want to meet when you're in the shower - or when your car has broken down in the middle of nowhere. In fact, not the sort of person you really want to meet anywhere, period. So psychopath dropped out of use in the world of psychology, who started using a new term for the same condition - sociopath. This new term gets away from the stigma that had been attached to the word psychopath through the popular media (because believe it or not, not all psychopaths are blood thirsty killers; like all mental ailments it comes in degrees) and also emphasizes the social nature of the illness. Now all the novelists and movie makers have caught on to the word sociopath, and are naturally using it instead now, and it's drifting into popular culture too. So sooner or later the psychologists will change the name again. This is a wordly arms race, and remember when we're on our fifth variant of 'psycho', that you heard it here first.