I'm 20yo with my sister (18yo) and my mother and stepdad in the house. It's 2am and I'm watching a movie from my bed. 

It's both exams for me and my sister, which means studying entire days. I got lucky by having a free day to watch a movie.

All of a sudden my sister walks into my room and asks if I could help her with the printer which wasn't working. I tell her no and that she shouldn't use the printer since it would wake up our parents. She proceeded to go to the printer room, with angry feet.

Our house doesn't have good sound isolation, so you can basically hear all doors and footsteps at night. This in combination with the sleep problems of our mom gives some troubled nights for her.

I follow her and angrily whisper that she should be quiet. She answers in a loud voice that I should just help her to print, being 7 meters away from our parents room. I whispered that she should shut up and started cussing at her (in whispering voice) that she was extremely disrespectful towards our parents. Then she started shouting, which made me gave her the bird and go back to my room to ignore her, so she would shut up.

Finally she left me with some messages saying 'With that aggression you'll never get a girlfriend' and 'Why do you always act like a dick to me'. As you might've guessed, similar situations have happened before.

I get that she needs to study and that I should've been less angry, but I think it's her fault for not printing at a normal time and that she could wait.

I think she's an asshole, but was I an asshole as well?