Psychopaths live largely undetected among us and if you're unfortunate enough to get entangled with one the results of their ruthlessness and manipulation can be devastating.
You can't tell just by looking at them. Psychopathic serial killer Ted Bundy was handsome, clean-cut and charismatic, and used these attributes to lure at least 30 women to their deaths.
What is a psychopath?
A psychopath isn't simply a nasty person, and, although Hollywood portrayals have promoted this perception, not all psychopaths are criminals. The following definition is from internationally renowned psychopathy researcher Robert Hare:
"A social predator who often charms and manipulates his or her way through life. Psychopaths are completely lacking in conscience and in feelings for others; they take what they want and do as they please without the slightest sense of guilt or regret."
Read: Understanding psychopaths
These are the main characteristics to be on the lookout for:
Callous lack of empathy
Probably the most significant characteristic of all, lack of empathy means that psychopaths are unable to understand and identify with the feelings of others. There is a cold lack of interest in someone else's pain or discomfort.
This is one of the main reasons psychopaths are so potentially dangerous: they can be cruel and callous because they aren't put off, as a normal person would be, by any sympathy for their victims' suffering.
Read: How alcohol affects empathy in men
Lack of empathy allows a psychopathic murderer to kill cold-bloodedly; but it may also allow a non-violent psychopath to trick aged parents out of their savings without remorse, for example, or to not hesitate before crushing a business competitor.
As Hare pointed out in his book Snakes in Suits, the modern capitalist world of business, which in many ways is geared towards rewarding ruthless behaviour, often allows functional psychopaths to rise through the ranks.
In fact, several psychopathic traits are prized in modern culture, says Hare:
"We live in a 'camouflage society'...in which some psychopathic traits - egocentricity, lack of concern for others, superficiality, style over substance, being 'cool', manipulativeness and so forth - increasingly are tolerated and even valued."
Conning, manipulation, deceit
Because psychopaths lack empathy, it's easy for them to view other people as mere objects to use for their personal gratification, and they have no qualms about lying and manipulating to get what they want.
Lying and conning comes easily to them too, because they don't feel the shame and anxiety about getting caught out that most of us would when being deceitful.
Lying is also helpful in creating what psychopathy pioneer Harvey Cleckley termed the "mask of sanity", which allows the psychopath to pass as normal.
Some psychopaths are past masters at spinning elaborate tales about themselves; others are less sophisticated and lie clumsily. When they do get caught out in a lie, however, they're highly unlikely to own up to it, will brush it off and try out new lies.
Read: How to spot a liar
Psychopaths don't only lack empathy, they lack normal emotional range and depth. They may feel some emotion, but only very superficially. Hare has described the emotions psychopaths do feel as "proto-emotions: primitive responses to immediate needs".
Read: Psychopathy, brain damage and empathy
They may appear stony and cold emotionally, but they also often feign emotions by observing normal people's responses, as part of the mask they show to the world. They learn how to imitate emotional reactions, although some are better at this than others, and they do sometimes slip up.
For example, they may learn how to use stock phrases of condolence when someone dies, but on their lips these can sound oddly mechanical.
Sometimes they misread situations and respond inappropriately, perhaps with a joke when a partner is trying to tell them something heartfelt.
Psychopaths may have sudden, brief emotional flare-ups, particularly of one emotion: rage. They can become explosively, violently angry if they don't get their way or feel they have been insulted or not treated with the respect they invariably believe they deserve.
These outbursts tend to be short-lived however, and, once over, the psychopath doesn't appreciate how much his behaviour might have upset those around him. He expects others to "get over it".
Psychopaths can be highly charming and persuasive, and smooth talkers. Many come across as confident, dominant personalities, even leaders (history is littered with psychopathic dictators).
Their charm can be very effective in attracting people initially, and this includes romantic and sexual attraction. Most psychopaths are men, and those who become romantically involved with them, primarily women, frequently become their victims.
Grandiose sense of self-worth
Psychopaths tend to have very high opinions of themselves, and think themselves better than others.
This further allows them to feel justified in using and manipulating people. Their inflated self-worth is coupled with a strong sense of entitlement to money, status symbols, or whatever they feel is owing to them.
Grandiosity may come across in some psychopaths as obviously boastful; others may exaggerate their previous accomplishments and abilities, or their future prospects of success.
Prone to boredom; thrill-seeking
Psychopaths have a low tolerance for boredom and an excessive need for excitement and stimulation, in part because they don't feel emotions, including fear, intensely.
This often leads to risk-taking and law-breaking; they may be drawn to take part in dangerous sports and activities, and have a high rate of drug abuse.
Impulsivity and irresponsibility
Psychopaths often act on the spur of the moment with little concern for the consequences of their actions. They often quit work with no alternative employment options, or suddenly end relationships, and tend to have histories of many job changes and multiple short romantic connections; they may have been married several times.
This is coupled with not taking responsibility for their behaviour; on the contrary, they will blame others when things go wrong.
True psychopaths are rare, and would be likely to possess several of the characteristics mentioned here (although not necessarily all). Some people may have psychopathic tendencies, or could be placed somewhere on the scale between normal and psychopath.Read more:
Psychopaths - inside the mind of a monster
Psychopaths - who are they really?
Does the SA law protect us against psychopaths?
Babiak, P and Hare, R. (2006) Snakes in Suits: When psychopaths go to work
Cleckley, H.M. (1941). The Mask of Sanity.
Hare, R. (1999). Without Conscience: The Disturbing World of the Psychopaths Among Us.