Most of us have had colleagues who can be tricky to work with.
They may act impulsively, be manipulative, or even outright lie to advance their careers - but how can you tell the difference between an unpleasant co-worker and someone displaying psychopathic traits?
Geraint Anderson, a former London banker-turned author, said he was assessed by a clinical psychologist who told him he may have had "situational psychopathy" in order to succeed in the cut-throat corporate world.
"I had to really become a kind of worse version of myself in order to thrive in this environment," he said.
Anderson, 53, who now lives in Monmouthshire, said some modern workplaces and social influences reward psychopathic traits.
He worked for 12 years as an analyst in London's financial district and earned millions of pounds before leaving his job ahead of the financial crash in 2008.
"The city rewards this dark triad behaviour... being uber confident, being able to control and manipulate others, not getting emotionally involved in decisions and being decisive," he said.
"I adapted myself for the city and started bringing out the kind of worst side of myself."
A psychopath is someone with an antisocial personality disorder, external, rather than a clinical diagnosis itself.
People with these disorders think and act differently to others and, among other things:
Exploit or manipulate others
Lack regret or remorse
Behave irresponsibly
Have difficulty sustaining long-term relationships
Are unable to control their anger
Lack guilt and blame others for problems in their lives
In his early 20s, Anderson was enjoying life in Goa, India, selling trinkets to tourists on the beach.
His brother convinced him to apply for a finance job, which he only intended to do for a few years.
"I cut off my ponytail, shaved off my beard, took all my earrings out, bought a £60 suit - all that's totally true - the day before I had my interview."
Once he had his foot in the door as an intern, success became an obsession, with bonuses becoming "a way of gauging how wonderfully successful a human being I was".
This figure allowed him to compare himself to people at other banks and "really appealed to my competitiveness".
He believes some of the traits that helped him climb the ranks were those associated with psychopathy.
"I had a degree of fearlessness. I had a bit of - dare I say - glib charm. I wasn't hugely emotionally affected by things that happened on the trading floor."
Anderson said a lot of traits psychopaths possess are ones "that the corporate environment rewards" and are "incredibly useful in high-powered jobs in the city".
He added the most important thing when it comes to psychopaths is "you don't promote them, you don't marry them and you don't vote for them."
Robert Snowden, a Cardiff University psychologist, has studied psychopathy for about 25 years and has worked with Robert Hare, the creator of the psychopathy checklist (PCL-R).
It consists of 20 questions, each scoring between zero and two, with a maximum score of 40.
Snowden said most people scored below five, while 25 or over was typically the threshold for psychopathy.
Anderson scored himself about an eight or a nine.
"Psychopathy is on a dimension that I could place you, I could place myself," Snowden said.
"They can be very strong and, in some ways, make good leaders... but there are many deficits to their leadership and it's all about them and not about other people," he added;
"The fundamental trait of psychopathy is that lack of empathy for other people.
"Most psychopaths never kill anybody. But they may take advantage of other people, exploit other people, not care about other people."
Snowden said some corporate environments may appeal to people with psychopathic traits as they often need "to be quite unemphatic" and focused on making money.
There is no treatment available for psychopathy, as "psychopaths often believe that there's nothing wrong with them".
Anderson was recently evaluated by Kerry Daynes, a consultant and forensic psychologist, who concluded he was not a psychopath.
Daynes said he may have become a "situational psychopath", adapting his behaviour to thrive in an environment that rewarded ruthless ambition.
She added: "You don't need to be a psychopath to thrive - for a while at least - in a psychopathic culture."
She said Anderson was able to "crank up" his "darker personality characteristics" to succeed in his environment, something that was in "the sweet spot that most people can't attain".
Despite rapidly rising through the ranks of London finance, Anderson said he became disillusioned by "greed, reckless risk-taking and rule breaking in the industry".
"I just looked around and thought 'I'm on the wrong team'... What on Earth are you doing? You are part of the problem."
He left and became the anonymous columnist City Boy, for the London Paper every Friday, revealing a world of excessive wining, dining, drugs and illicit sex.
It transformed into a the book Cityboy that sold more than 400,000 copies and was translated into six languages.
He's also recently just published his fifth book which explores how adopting psychopathic traits can help people climb the corporate ladder.
Anderson said he was a "less pleasant person" while in the corporate world but hopes he is a "warmer person" now
"I'm more able to feel like trying to have integrity and not manipulate and be ruthless."
Although, he joked, his wife may disagree about him not having any of his psychopathic traits left.
