(CNN) -- NFL offensive lineman Richie Incognito has been on the defense since November after fellow Miami Dolphins player Jonathan Martin abruptly left the team citing emotional abuse by Incognito on and off the field.
Incognito adamantly maintains the two were friends who just had a crass rapport, though an NFL-sanctioned investigation found racial slurs used by Incognito and sexually explicit messages about Martin's mother and sister constituted a "pattern of harassment." The report also concluded that the two developed "an odd but seemingly close friendship."
Incognito took to Twitter in a series of messages on February 12 to clear his name, including: "I'm ready to move on with my life and career. I've been dragged through the mud for months by my 'best friend'. #betrayed #railroaded."
I'm guilty of being a loyal friend and good teammate. I apologize for my poor language and rude remarks. I've never denied it.— Richie Incognito (@68INCOGNITO) February 12, 2014
He would publicly apologize online -- again -- to Martin less than five days later.
The public beef has caused some to question Martin's toughness and others to examine the harsh environment of the pro sports locker room. But it's also worth acknowledging that the dynamic between Incognito and Martin isn't so rare -- many of us have been embroiled in what pop psychology would call a "toxic friendship."
For Iz Zakaria's 21st birthday, her good friend of more than 10 years sent her a self-help book on dating -- effectively throwing a burning match into the powder keg that was their relationship since seventh grade.
"It seems tiny and ridiculous, but it came near graduation, when I was facing the prospect of being unemployed and moving back home," Zakaria, now 22, wrote in an e-mail to CNN from Brunei. "It was a reminder of another part of life that I am failing at -- my love life."
Zakaria wrote about her "toxic friendship" and subsequent fallout on the Web journal Thought Catalog.
She attributes her self-deprecating sense of humor and fear of confrontation, in part, to the pair's drawn-out, dysfunctional accord.
"Most of the time, she exploited that, she built on those jokes and got everyone to laugh at me," she says. "She made me feel like I knew nothing, that I was a child and I was immature."
What made the dynamic even more confusing, and complicated to stop, is that there were, of course, jolly times -- especially when nobody else was around to impress. But the dating book was the final chapter in their storied love-hate relationship.
"You can't keep victimizing yourself like that," she says.
Communication expert Lillian Glass decided to pen the book "Toxic People: 10 Ways of Dealing With People Who Make Your Life Miserable" after hearing many tales like Zakaria's.
"The definition of friendship is admiration and respect, and if you don't have those two, you have nothing," Glass told CNN.
There are two types of toxic friendships, says Glass: Those that start out toxic, and those that start to require a Hazmat suit over time.
When a friendship starts out overly contentious or competitive, it's worth asking why you're pursuing it in the first place. You might be recreating an unhealthy pattern, perhaps modeling your relationship with a parent who belittled you as a stand-in for showing affection.
"Sometimes what we don't resolve, we repeat," Glass says.
On the other hand, pals can simply evolve in opposite directions -- this is particularly true in friendships that have endured since adolescence. Change, though, isn't inherently a bad thing. It's more when there is a "discrepancy in personality and values" or a friend discourages success, says psychologist Irene S. Levine.
Levine also wrote a book on prickly pacts, titled "Best Friends Forever: Surviving a Breakup with Your Best Friend."
"Since friendships are voluntary relationships, it makes no sense that they bring you down," she says. She stresses in the book that people make many friends in life but only a few stick for prolonged periods.
Those long-standing bonds, Levine says, are particularly hard to navigate -- or end -- because of the significant losses in cutting ties.
"These people are like scrapbooks of our lives, collection of our memories. It's very nice to be able to reminisce and have someone know your roots and know you in a different phase," she says.
An uncordial split could put mutual friends in an awkward situation. If the toxic friend's nature is spiteful or vengeful, there's also the potential that he or she could unleash a firestorm of secrets and confidences you shared through the years.
But, Glass says, if that's their nature, they're probably already talking behind your back.
"Deny it or ignore it and distance yourself," she says. "Then again, as they say, don't tell your best friend what you wouldn't want your worst enemy to know."
Short of "dumping" the friend, Levine suggests there are other ways to attempt to ease the tension: Take a break from the person by speaking and seeing them less frequently.
If the other party is persistent or guilt-trips you for not being around, a little white lie about scheduling could be in order.
Levine says it's nice to want to maintain a longtime connection, but if none of these fixes work, the offended party must find a way to end it.
Although it might be hard to address awkwardness, try to be direct but ultimately kind. And never end a friendship impulsively.
"You really need to think very carefully before you do it," Levine says. "There's no going back. People will never forget that conversation."
Are you or have you been in a toxic relationship? Did you make amends or call it quits? Share your experiences in the comments below.