Billy Nolan was a low class sociopath bordering on psychotic. Hargensen herself was a spoiled narcissistic bully. Billy was abusive and that would have been conditioned onto him from a young age.
As the book explains though, Billy's rough edged persona excited Chris. He was in a sense her equal and he even superseded her, because she wasn't the one really in control, he was. She used sex to manipulate him. Even then, he would have dominated.
Norman! What did you put in my tea?

I would have loved to see that

Nancy Allen had said in and interview that there was a scene that they cut from the film when Travolta's character violently rips her top off in the car after he had hit her.
So, they actually toned it down.
Are you okay?

She was used to being slapped by Billy, but the real clincher was when Miss Collins did it to her. That was in a different ballpark. It only made its impact on her because another female did to her and an authority figure.
That was one slap that was truly deserved, even though Collins reacted in a manner that would be considered inappropriate for a teacher.
Norman! What did you put in my tea?

Because she deserved it

He was not a good person.
So many stories, so little time.

Awful thing to do, anyway