Like a Boy Toy, except its referring to a girl.
Boy 1: I've been hooking up with her for weeks.
Boy 2: So is she your girl twirl?
Boy 1: yeah...
Like Boing-flip, if somebody insults you, this 'twirls' it back in their face, in a girlry fashion.
Alex: Ella smells!
Ella: Girl twirl!