Me (12F) and my half-sister (4) have never understood us because of their father. She is a really spoiled child and she always becomes love while my mum and stepfather yell at me because of nothing. But anyways. Yesterday my mum cooked lasagna. I was in my room and have done some school work. It already was a bad day and I was pretty pissed. After a while my mum screamed "dinner is ready. Put your ass down here". I just grumbled and gone downstairs. My mum and my sister already sat on the table so I silently put a little bit of the lasagna on my plate. My mum had already made some milk for me and my sister. I silently eat my lasagna while my mum called my stepfather and my sister drinks her milk. After a while my sister spits the milk out. Fully into my face. I totally yelled at her because she done it on purpose. Then my mum start to yell at me and called me an accident that she regrets every day. I was totally upset but later that night I couldn't sleep. I was totally sorry that I yelled at my sister and the regret killed me. So am I the asshole?