A really fucking annoying person that is someone's younger sibling and is a girl at the same time. Usually annoys the shit out of their older sibling and the older sibling's friends.
Boy1: Holy shit, your sister is so fucking annoying.
Boy2: I know right? I wish I didn't have a little sister.
Boy1: Yeah, she always walks in on us when we're playing games and she never fucking leaves us alone.