I just slapped my girlfriend hard across the face and she cried a little.
Is there a reason you slapped her?
I just didn't like the way she tried to give me a lot of crap I'm not interested in.
You shouldn't slap your girlfriend over an argument. This is assault and you should be arrested for it.
It's fine, lots of bdsm couples act like that so it's honest and that's how it should be.
If you're not in a relationship like that, you shouldn't hurt your girlfriend by slapping her in the face. If she's upsetting you, you should talk to her instead of escalating things.