It’s not okay that a boy I was sleeping with in college had plans for anal sex without telling me. I was so shocked that he started to do it without my consent, that aside from some wincing and uncomfortable groans, which I know he saw, I said nothing. He met my pain with silence, too, and continued despite my obvious apprehension. (Not necessarily saying this is assault, but still pretty NOT okay, nontheless.)
The Night it Happened
Molly S. Hill

This is absolutely assault. And very much not ok.