Sociopath is quite a general term, that covers a variety of very similar disorders. While we can go and look up the ways to diagnose someone, in everyday life and without proper training, we can't really make clinical assessments. We can be easily wrong if we attempt to judge people, and it's a small step from there to become prejudiced. The training involved in psychology gives a fuller understanding, enabling psychologists and psychiatrists to look at things more objectively. Instead, I've found it helpful to look upon the measures and 'symptoms' themselves, and just treat them as personality traits of the individuals I know. Mental disorders are often exaggerated or distorted versions of traits we all have to some degree. For example, most people worry about what other people think - some not so much, others a lot, some worry about things that might not be true, or what might come true - but at what point does it start becoming a symptom of paranoia? And does it really matter? Does it negatively effect their life in any way? It's a complex sliding scale with lots of factors to consider. The same is true of sociopatic, psychopathic, antisocial and dissocial personality disorders. We can look at, for example, the lack of empathy, and to a certain degree everyone has that. It's a survival trait, since we can't care about all people or situations, all of the time. How do we tell if someone's struggling to understand, or prioritising differently, or simply incapable? There's "lack of remorse," "prone to violence," "superficial charm," "manipulation"... but these are all facets of humanity. Does a sales-person's pitch count as manipulation and superficial charm? Is a person who's grown up in a violent society necessarily a sociopath, or is the violence they resort to another facet of how they were brought up? I've met a few people who match a few of the flags for this sort of disorder, but it helped me realise that they're not sociopaths, they're just a bit further along on the 'sliding scale' for some factors, the same way the next person you meet could be the complete opposite. It's very helpful when it comes to learning what makes people tick. What counts as 'normal' is a pretty broad brush, for us humans. Sorry, I think I went slightly off topic.

As a gross (& terse) 'rule of thumb', someone who consistently 'takes' more than he 'gives', emotionally, economically & socially.

Most sociopaths know how to conceal their disorder quite well. They will behave as normal people do, feigning emotional responses they don't truly feel, knowing what words will make them sound compassionate, recognizing the moments empathy is appropriate, and to the outside world they will appear to have a conscious like everyone else. But inside, they feel nothing. The only way to recognize a true sociopath might shock some people, but it is the one thing they do impulsively and have no control over: The pity party. Sociopaths love to garner your pity. They have no quams about appearing as victims to other people, that they are suffering in some way. If you want to peg a sociopath, watch to see if they actively pursue pity from other people.