Could that amazing new person you or a loved one is dating actually be a sociopath? It's not as far-fetched as you might imagine. Roughly one in 25 Americans is a sociopath, according to Harvard psychologist Dr. Martha Stout, author of The Sociopath Next Door.
Of course, not all sociopaths are dangerous criminals. But they certainly can make life difficult, given that the defining characteristic of sociopathy is antisocial behavior.
Here are 11 RED FLAGS to look out for:
RED FLAG #1. Having an oversized ego.
The Diagnostic and Statistical Manual of Mental Disorders (DSM-V) notes that sociopaths have an inflated sense of self. They are narcissists to the extreme, with a huge sense of entitlement, Dr. Seth Meyers, a clinical psychologist with the L.A. County Department of Mental Health, wrote for Psychology Today. They tend to blame others for their own failures. 
RED FLAG #2. Lying and exhibiting manipulative behavior.
Sociopaths use deceit and manipulation on a regular basis. Why? "Lying for the sake of lying. Lying just to see whether you can trick people. And sometimes telling larger lies to get larger effects," Dr. Stout told Interview Magazine.
RED FLAG #3. Exhibiting a lack of empathy.
“They don’t really have the meaningful emotional inner worlds that most people have and perhaps because of that they can't really imagine or feel the emotional worlds of other people," M. E. Thomas, a diagnosed sociopath and author of Confessions Of A Sociopath, told NPR. "It’s very foreign to them.”
RED FLAG #4. Showing a lack of remorse or shame.
The DSM-V entry on antisocial personality disorder indicates that sociopaths lack remorse, guilt or shame.
RED FLAG #5. Staying eerily calm in scary or dangerous situations.
A sociopath might not be anxious following a car accident, for instance, M.E. Thomas said. And experiments have shown that while normal people show fear when they see disturbing images or are threatened with electric shocks, sociopaths tend not to.
RED FLAG #6. Behaving irresponsibly or with extreme impulsivity.
Sociopaths bounce from goal to goal, and act on the spur of the moment, according to the DSM. They can be irresponsible when it comes to their finances and their obligations to other people.
RED FLAG #7. Having few friends.
Sociopaths tend not to have friends--not real ones, anyway. "Sociopaths don’t want friends, unless they need them. Or all of their friends are superficially connected with them, friends by association," psychotherapist Ross Rosenberg, author of the Human Magnet Syndrome, told The Huffington Post.
RED FLAG #8. Being charming--but only superfically.
Sociopaths can be very charismatic and friendly -- because they know it will help them get what they want. “They are expert con artists and always have a secret agenda,” Rosenberg said. "People are so amazed when they find that someone is a sociopath because they’re so amazingly effective at blending in. They’re masters of disguise. Their main tool to keep them from being discovered is a creation of an outer personality."
As M.E. Thomas described in a post for Psychology Today: "You would like me if you met me. I have the kind of smile that is common among television show characters and rare in real life, perfect in its sparkly teeth dimensions and ability to express pleasant invitation."
RED FLAG #9. Living by the "pleasure principle."
"If it feels good and they are able to avoid consequences, they will do it! They live their life in the fast lane -- to the extreme -- seeking stimulation, excitement and pleasure from wherever they can get it," Rosenberg wrote in Human Magnet Syndrome.
RED FLAG #10. Showing disregard for societal norms.
They break rules and laws because they don't believe society's rules apply to them, psychiatrist Dr. Dale Archer wrote in a blog on Psychology Today.
RED FLAG #11. Having "intense" eyes.
Sociopaths have no problem with maintaining uninterrupted eye contact. "Our failure to look away politely is also perceived as being aggressive or seductive," M.E. Thomas wrote for Psychology Today.