Spotting toxicity in a workplace isn't hard given its prevalence (an astounding 76 percent of bosses are considered toxic by their employees). But spotting what causes it, the unspoken rules embedded in a culture or the specific employee traits most likely to lead to toxic behavior, can be trickier.

Unless you follow the findings of a 2015 groundbreaking study on workplace toxicity conducted at Harvard University. The study came back into the limelight at a recent event I keynoted, with exasperated clients after the talk asking me how to address a toxic culture that was emerging at their company.

Here's why it matters. The Harvard study, for the first time, pegged a financial number to solving the problem of the toxic employee (defined as one who engages in behavior that damages the company or fellow employees).

Specifically, while a top worker can return more than $5,000 in cost savings to a company through increased output, avoiding hiring or "fixing" a toxic employee nets well over $12,000 in savings (not including savings from avoiding litigation, regulatory penalties, or decreased productivity in other employees because of low morale induced by the toxic individual).

The money factor pales in comparison with the overall damage caused--other employees quitting at a faster and more frequent rate, a loss of customers, and the tanking of a culture.

Now, about spotting the kind of behavior that will most commonly lead to toxic behavior. Here's what the study found are the three big warning flags:

1. An excessive level of self-centeredness

In other words, someone who is highly selfish by definition doesn't care about others. Which means they certainly won't care how their behavior or attitude affects co-workers.

Even worse are the selfish employees who have zero self-awareness or inkling that they're coming across as a self-centered you-know-what. So employees who consistently act in selfish ways should send a signal flare that compounding toxic behavior lies ahead.

2. An excessive level of confidence

Overconfidence leads to undue risk-taking with destructive behaviors. As Dylan Minor, co-lead on the study told the Harvard Gazette: "Imagine you're going to engage in some misconduct and steal something from your company. If you think the chance that you're going to get away with it is much greater than it really is, you're more likely to engage in that conduct."

This is the same mentality that leads brash criminals to commit stupid crimes--they don't think they'll get caught. Overconfidence plays out in more subtle ways, too; the employee thinks they're clever enough to fire off barbs and doses of negativity without their corrosive patterns being spotted or reprimanded.

This issue is exacerbated by the fact that Dylan's research also shows that overconfident-to-the-point-of-toxic employees tend to be highly productive. So their behavior often goes unaddressed, which is brutal on broader employee morale.

3. Emphatic pronouncements that "rules should always be followed"

This one is counterintuitive. You'd think rule followers would do just that in culturally friendly ways. Dylan explains: "But I find very strong evidence in my study that those that say 'Oh, no, you should always follow the rules' versus those that say 'Sometimes you have to break the rules to do a good job' are much more likely to be terminated for breaking the rules."

It's a way for the supposed rule followers to visibly and verbally throw people off their scent, or to articulate the way they know they should act to ease their guilt for knowing they're actually going to do the opposite of what they proclaim.

What good comes from knowing these signs of bad?

Knowing these three warning signs serves as another discerning factor to watch for in interviews to help avoid bringing "high toxic potentials" into your organization.

Spotting these signs in current employees gives you a hit list of behaviors to keep an eye on or to proactively address. Doing so cuts off the behaviors' direct and indirect impact (discouraging others from behaving the same way).

The study found that without question, the worst thing you can do is nothing. Unaddressed toxicity has a corrosive impact on surrounding employees who will feel unsupported and will conclude that accountability in the company is absent.

So watch for these signs and post a sign of your own: "Not Wanted."