“The bedbugs are a metaphor,” Karpf wrote on Monday. “The bedbugs are Bret Stephens.”

The tweet got nine total likes and zero retweets, Karpf said. So the professor was surprised when an email from Stephens himself popped in a few hours later.

Then, he noticed his provost at GWU was copied on the email. And Stephens was furious.

“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.”