Girls, my sister pantsed her friend in front of me, what should I do?

So my younger sister's friend was over this weekend and according to my sister her friend has a crush on me. My sister can be kinda a jerk sometimes. So they were standing in the kitchen and her friend was facing away from me reaching for something. My sister decided to yank her basketball shorts down to her knees (her panties came down too actually) and pull up her shirt. While doing this she yelled my name so i turned and saw her friends naked butt. She then asked if i enjoyed the view and laughed and I told her she was a jerk. her friend was obviously super embarrassed and i feel kinda bad about it. should i say something to her friend?
Girls, my sister pantsed her friend in front of me, what should I do?
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