A US psychology professor has apologised after causing outrage after a live sex toy demonstration was given to his class.

John Michael Bailey, 53, admitted fault over the graphic display where a woman stripped off and was penetrated with a sex toy by a man.

Neither was a student at Northwestern University.

The seminar was meant to be a supplemental and optional addition to Bailey’s regularly scheduled human sexuality course.

The professor forewarned students attending the seminar that it would be explicit, but claims the sex act was completely unplanned, although allowed it to take place when he “couldn’t think of a reason why students shouldn’t see it.”

Nearly 100 students from the 600-person lecture stayed after class to learn from what Bailey called an extracurricular seminar on “Kink and Fetish” on 21 February.

The unplanned sex act has the University divided about the limits of academic freedom, although over 800 NU students have signed a petition requesting that Bailey not be fired for the incident. But the university’s higher ups are taking the demonstration more seriously in an effort to preserve their elite school’s reputation.

University President Morton Schapiro said Bailey showed “extremely poor judgment” in allowing the sex act.

Bailey’s written apology expressed regret over the incident’s fallout, but not the educational benefits that the impromptu sex act provided.

“I regret allowing the controversial after class demonstration on February 21st. I regret the effect that this has had on Northwestern University’s reputation, and I regret upsetting so many people in this particular manner. I apologize,” wrote Bailey.

A student from the class has claimed the incident wasn’t ideal, but not necessarily out of line.

“It’s unfortunate. I personally, I wouldn’t say I liked the demonstration but I saw educational benefit in it,” said the student, “It’s Professor Bailey’s class. We’ve watched videos that are far more explicit than that from time to time.”