If someone at the office is making you feel consistently drained, stressed or unmotivated, you might be dealing with a toxic coworker.
That's according to Stanford University professor and bestselling author Robert Sutton, who's devoted years to the study of mean employees.
"Over the course of our lifetimes," he tells CNBC Make It, "about 50 percent of us will face persistent bullying or observe it regularly in the workplace."
Whether this person pretends to be your friend one-on-one, then quietly undermines you in front of your boss or sends you rude emails, they can impact your productivity and your health.
So how do you deal with this type of coworker?
Changing how you react mentally, or using psychological tricks, can significantly help, says Sutton, organizational psychologist and the author of "The A-----e Survival Guide."
When used with other helpful strategies, like telling your HR manager, these tips can help you create a mental barrier between you and an unkind colleague:
1. Rise above it
"If you're exposed to this constantly and you can't stop it," Sutton says you should tell yourself things like "it doesn't matter," or, "it's not me, it's them."
Some office bullies are just looking for a fight, he says. If you can ignore their rudeness and continue to work despite their aggression, try to do so.
2. Don't take it personally
A toxic coworker can leave you feeling down for hours or even days after they do something mean. To prevent that, imagine a wall between you and the person, the psychologist suggests.
Tell yourself, "I can't take it personally," Sutton writes.
3. Remind yourself that you're not alone
If a bad apple at work is unkind to you, chances are they're mean to others, too. Realizing this will help you avoid blaming yourself for his or her actions, Sutton says.
You can tell yourself things like, "I am not crazy or a bad person," he writes.
In addition, try to surround yourself with friendlier people at the office and avoid being physically near the toxic coworker.
4. Use emotional detachment
One of Sutton's favorite mental strategies is to practice emotional detachment.
"One of my colleagues at Stanford uses this," he says. "It's to pretend you're a doctor who studies a------s and look at the various forms and to catalog them."
In this sense, you create a mental game for yourself, where you observe a toxic coworker's behavior like an explorer would observe an animal in the wild. This can help you tune them out.
5. Remember, it's temporary
While you shouldn't just get up and quit your job, you can remind yourself that you have options for getting out of the bad situation. Consider trying to move departments within your company or start applying to other jobs.
Tell yourself, "it will all seem like no big deal when I look back at it later," Sutton writes.
However, it's important to know that there are certain cases where mental strategies alone aren't enough. If a coworker is preventing you from doing your work, creating an unsafe environment or harassing you, discuss it with your HR manager or boss right away.
Having a strong mental attitude, in addition to taking any other necessary action, will help you feel happier and more productive, Sutton says.
"Practicing the fine art of not giving a s--t about people who mistreat you," he writes, "can save your sanity, shield your physical health and keep you from hurting the people you love."
Video by Richard Washington.
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