Is it normal to get mad about this?

Okay. I got in trouble because I got mad at my little brother for opening the door while I was dressing up. He's fully aware that the door knob is broken yet he opened the door without knocking. He did this twice actually, but the last time it happened, I was fast enough to grab my towel and cover myself. But this time, my towel wasn't there and I was just sitting there naked putting on some lotion. He said he didnt see anything but my brother lies a lot so I doubt it. I got mad. So I stood up, wrap my body with towel, went outside and hit his head. It was more like pushing, actually, rather than hitting. I usually do it as a sign of my affection (when he was younger) so I know it didn't hurt. However, my mother overreacted and took my brother's side, saying that I'm rude and violent and said "...as if your body is made of gold for you to react that way." I was thinking "Oh, so I should parade my body in front of everyone because my body is NOT made of gold?" She didn't even tell him to apologize for opening the door without knocking.