How does rolling your eyes (out of boredom) merits a backhand?

I'm not speaking with my grandmother at this point because she did this. Plus that kind of hard for a woman. It landed on my nose and cause a bit of nosebleed.

I angrily told her ''I'm freaking bleeding, I hate you'' and slammed my bedroom door. I was bored with politics conversation, had a stressful day at school and now this. I felt assaulted to be honest. Just for rolling my eyes, does it merit getting physical with a backhand enough to get you a nosebleed? Too much. I never got backhanded in my life, much less like that. I hate her.

Now I lost even more respect for her. My parents didn't like what she did either and are having a very serious conversation with her.

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I really don't understand how would that even make me respect her? It actually makes me hate her right now.
How does rolling your eyes (out of boredom) merits a backhand?
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