While his "joke" is old fare, i dont think its particulary Rabelaisian, and certainly not offensive.
But...
...when you crack a joke to a Professor of Gender studies, prepare for blowback.
While i dont think it warranted a complaint, he certainly hasnt helped himself by "adding insult to injury".
https://reason.com/blog/2018/05/08/joke-elevator-lebow-sharoni/amp?__twitter_impression=true
The old stick is now doubling down and refusing to apologise.