Well, I'll tell you the back story of Ahegao faces or commonly called the O-face in Japanese porno scene.
Ahegao, is a popular facial expression that originated from Japanese erotica written by a man who fantasized about assaulting children. It plays off and reinforces the stereotypes that Japanese women are submissive, easily overpowered/manipulated, and that they want/deserve abusive treatment.
It was later used by other artists to portray lust, submission and desire.
What you saw in shit-tok is just a gen z version.