Wikipedia Sucks!

It's a word bandied about a lot so I thought I'd summarise a popular article on the subject

Current approach is to use a list of criteria.

1. Uncaring -- callous unconcern for feelings of others. Poor at detecting fear in others. High threshold of disgust
2. Shallow emotions -- such as shame, guilt, embarassment
3. Irresponsibility -- lack sense of shame or remorse
4. Insincere speech -- shallow sense of word meaning, trouble understanding metaphors and abstractions
5. Overconfidence -- grandiose sense of self-worth
6. Narrowing of attention -- impulsive
7. Selfishness -- pathological egocentricity
8. Inability to plan for the future
9. Violence -- irritable, aggressive, intolerant of frustration

That's the "textbook" definition and it works well enough. But to see how it is poorly dealt with in the "real world", I recommend reading Jon Ronson's The Psychopath Test. He talks about the ugly mess that resulted when the British medical establishment started administering the Hare Psychopathy Checklist to people, and involuntarily committing a few of them as "criminal psychopaths" for simply "failing-or-whatever" that test. (Robert Hare, who makes money from licensed use of his test, absolutely hated that book and has written long screeds condemning it. Must have struck a nerve.)

A perfect of example of psychiatry being used as an "inquisition". Ultimately most of these disputes boil down to one thing: $$$$$