On Twitter Monday afternoon, a George Washington University professor compared conservative New York Times columnist Bret Stephens to a bedbug after a Times editor had posted that bedbugs were spotted in its newsroom.

David Karpf's tweet, which read, "The bedbugs are a metaphor. The bedbugs are Bret Stephens," initially gained little traction. But Stephens took notice, and escalated his complaint about the tweet to Karpf's boss at the university.

"This afternoon, I tweeted a brief joke about a well-known NYT op-Ed columnist," Karpf wrote Monday night. "It got 9 likes and 0 retweets. I did not @ him. He does not follow me. He just emailed me, cc’ing my university provost. He is deeply offended that I called him a metaphorical bedbug."

The exchange went viral soon after, when Karpf posted Stephens' full email on Twitter.

"I'm often amazed about the things supposedly decent people are prepared to say about other people — people they’ve never met — on Twitter. I think you’ve set a new standard,” Stephens wrote. "I would welcome the opportunity for you to come to my home, meet my wife and kids, talk to us for a few minutes, and then call me a 'bedbug' to my face. That would take some genuine courage and intellectual integrity on your part. I promise to be courteous no matter what you have to say."

"Maybe it will make you feel better about yourself," Stephens continued. "Please consider this a standing invitation. You are more than welcome to bring your significant other."

By Tuesday morning, with the ordeal becoming one of the highest trending subjects on Twitter, Stephens opted to delete his Twitter account.

"Time to do what I long ago promised to do," the columnist wrote. "Twitter is a sewer. It brings out the worst in humanity. I sincerely apologize for any part I've played in making it worse, and to anyone I've ever hurt. Thanks to all of my followers, but I'm deactivating this account."

Stephens, an MSNBC contributor, was then asked about the spat by network host Chris Jansing on the air Tuesday morning. Stephens said being compared to a bedbug was "dehumanizing" and "totally unacceptable."

"Analogizing people to insects is always wrong," Stephens said, adding there is a "bad history" of comparing humans to insects that "goes back to a lot of totalitarian regimes in the past."

The columnist added that he was not trying to get the professor in trouble by copying the university provost on his email, but said higher-ups at universities, businesses and major media outlets should be aware of how their employees interact online with others.

Reached over email by NBC News on Tuesday, Karpf said he was surprised by Stephens' answer on MSNBC.

"He does not seem to understand what he did wrong here, or take any responsibility for his behavior," Karpf said. "The tweet would have languished in obscurity had he not felt the compulsion to find it, find me, and then find a way to pressure me by cc'ing the university provost. It speaks poorly of his judgment. The Times ought to have a conversation with him about his behavior."

Forrest Maltzman, the university provost, on Tuesday responded to Stephens in an email, a copy of which Karpf provided to NBC News.

"As you know, as an academic, Professor Karpf speaks for himself and does not take direction from me," Maltzman wrote. "His opinions are his own. Our commitment to academic freedom and free speech are integral to GW's mission. I see on Twitter that you invited him to your home. I would like to take this opportunity to invite you to come to our campus to speak about civil discourse in the digital age. Please reach out to me if this is of interest."

Stephens' commentary has long been a source of criticism among liberals, who have disagreed with his takes on free speech, climate change and millennials. When Stephens was at The Wall Street Journal, he once wrote that anti-Semitism was "the disease of the Arab mind."

Some minority and female writers and commentators took issue on Twitter with Stephens having such a strong reaction to being called a bedbug, contrasting that insult with some of the invectives hurled at them.

It probably is a bummer to be called a bedbug but people have written to me that they hope I get raped. Must be nice to get insulting comments and feel comfortable inviting the person to your home! — Elise Foley (@elisefoley) August 27, 2019

It probably is a bummer to be called a bedbug but people have written to me that they hope I get raped. Must be nice to get insulting comments and feel comfortable inviting the person to your home! — Elise Foley (@elisefoley) August 27, 2019

As every woman and person of color is trying to tell Bret Stephens, nearly every hate mention we get would be IMPROVED if they replaced the bad words with "bedbugs."

I recently wrote about some of the mail I receive, in case Mr. Fragility is interested.https://t.co/HGIiCeDjWy — Elie Mystal (@ElieNYC) August 27, 2019

If Bret Stephens is offended by being called a “bed bug,” then he should see the list of words I’ve filtered out of my mentions. White fragility is real, and we should all really stop accommodating it. — Evette Dionne 🏁 (@freeblackgirl) August 27, 2019

Bret Stephens freaks out that a professor mocked him by calling him a "bedbug" and tries to get the guy fired. I wish That's the worst I got called for my articles. Instead Ive literally had Trump loving Neo Nazis threaten to kill me for daring to criticize Trump. #ByeByeBret — (((DeanObeidallah))) (@DeanObeidallah) August 27, 2019

Stephens' exchange with Karpf was not the first time he has hit back at a critic over email. Stephens did not immediately respond to a request for comment.