A question to the ladies about my sister dressing skimpy?

I am a 22 year old male college student and recently my 19 year old sister moved in with me because we go to the same college out of state. She is a really friendly girl and plays vollyball at school. My question is in regards to how she dresses around me. She always dresses really skimpy out of the house but in the house it's even worse. She is always wearing tiny skirts and when she is sitting i can see her panties. She also wears really small shorts were the bottom of her *** hangs out of them. i really try my hardest not to look but it is just so out there. If she noticed i glanced at her she just sticks it out more and says something like "do these make my look big" and it is becoming harder and harder not to look at her. She has even came into my room to use my CPU in just her boyshorts, i could make out and everything/ My question to the ladies is, have you ever dressed really skimpy in front of your brother and if so, did you care if he looked?