My sister's friend came over, and her tight, round butt made her panties dig in deeply, so she kept adjusting them by slipping her hand under her skirt. Without realizing it, her panties became completely visible, and the way she blushed was absolutely irresistible. But she actually enjoyed being watched and started showing off even more. Taking advantage of the opportunity, we had a delicious time together, and my sister seemed to enjoy it too.