When a sister has or garners friends that unbeknown to her are in the friendship to meet said sisters brothers. Can be incredibly awkward when you invite a friend over to play my little ponies and the friend is more interested in the brothers comings and goings. Typically the younger sister of two or more brothers, but can be applied to older sisters as well. Usually occurs around first grade for the sisters when the brother pretends he is helping make a mud-pie, but in truth has an agenda to make the new friend the recipient of his first kiss. This anomaly can continue into adulthood. Often results will be marriage and children....
Interested Friend: Wow work was hard today. Hey who were those boys that came into to see you?
Wing-sister: Oh that was my brother and cousin.
Interested Friend: Hey wanna hang out soon?
Brother: Hey you know that one chick you hang out with?
Wing-sister: Yeah we are going to make mud pies for Mom today.
Brother: Need some help?