I've had a few GFs hit me at one time or another for varying reasons. Always because of a comment.

One day, I was reading a book, on the far side of our large bed. GF said something. I replied while reading. Then she heel dropped me in the shoulder. It fucking hurt. I don't even remember the conversation, but violence wasn't even in the ballpark. After recoiling from the first surprise attack, I saw the second same attack coming. I swatted it aside and punched her in the thigh. Pretty much giving her a charlie horse. That stopped her. She sat on the bed rubbed her thigh, I rubbed my collar bone. And that was that. It was over a decade ago, but yeah, that shit happened. I hit a girl.