About one to two percent of people in the general population are psychopaths (that percentage is higher in prisons, boardrooms, and undergrad economics classes). Which means that if you have more than a hundred friends on Facebook, there's a good chance one of them is a psychopath.

But which one? Science is hard at work on the question, with various researchers looking into telltale signs that someone on social media is a psychopath. Though this work is far from definitive, they've already some up with a few red flags you can look out for.

1. Trolling, bullying, or posting violent or pornographic content

The first tell is the most obvious. Probably no one was shocked when scientists demonstrated that those who post hate-filled comments and intentionally rile people up online tend to have psychopathic tendencies.

"The research, conducted by Erin Buckels of the University of Manitoba and two colleagues, sought to directly investigate whether people who engage in trolling are characterized by personality traits that fall in the so-called Dark Tetrad," reports Slate. "It is hard to overplay the results: The study found correlations, sometimes quite significant, between these traits and trolling behavior."

Likewise, Swedish scientists have confirmed that people who post violent or pornographic material also tend to be psychopaths. Not that this really needed confirmation.

2. Men who take lots of selfies

The rest of the tells, however, are less intuitive. For instance, a team out of Ohio State University has demonstrated that men in particular who post a ton of selfies are more likely to display psychopathic tendencies. (Sorry, Justin Bieber).

3. Those obsessed with food and other pleasures  

Perhaps you've wondered why some people feel compelled to constantly share pictures of their meals? Given that science shows psychopaths are weirdly interested in talking about food and other physical satisfactions, one reason just might be their dark personality. (Though plenty of others, I'm sure, are just really stoked about their dumplings.)

"According to one study of 6,724 participants, published in the journal Computers in Human Behavior, people who score high in psychopathy personality tests often write posts relating to their own needs and satisfaction," reports Business Insider.

4. Stirring up political flame wars

If everyone who ever posted a political rant on Facebook was a psychopath, I and just about every one of my friends would qualify. But according to the same research cited by BI, an obsessive interest in politics can actually be a sign of psychopathic tendencies

Why do psychopaths love talking politics on social media? "One interpretation is that psychopathic individuals are attracted to these topics because they revolve around issues of power, authority, and conflict that they might find particularly attractive," the study authors note. "In addition, these topics on social media are often rife with conflict and may provide a venue for aggressive online behaviors that psychopathic individuals are prone to engage in."

So worry less about someone who posts the occasional tearful lament about the state of the country or reminder to attend a rally, and more about that guy who seems to be using politics to pick fights and upset people.

5. Staying friends with your ex

Perhaps the weirdest sign of a social media psychopath is this one uncovered by a pair of Oakland University researchers. Apparently, the seemingly nice decision to maintain friendships with an ex can actually be a sign of psychopathy. This sort of Facebook psycho isn't staying in touch with old flames for sentimental reasons, but instead out of hopes of milking something more out of the relationship.

"People who had 'measures of dark personality' were more likely to maintain relationships with their exes for 'practical and sexual reasons,'" reports Medical Daily.

As an extra bonus, science has also uncovered one social media behavior that is decisively linked with not being a psychopath. Apparently, if any friends have shared their love of books on Facebook, you can cross them off your list of potential psychos. 

In one study, "the number of books 'liked' on Facebook profiles was negatively correlated with [psychopathy]--a finding the authors suggested might indicate that an interest in books contradicts psychopathic tendencies such as thrill seeking, impulsivity, and affect deficiencies," reports Psychology Today.