The girls?

Did I totally miss a turn somewhere?  When did it become commonplace to refer to breasts as "the girls"?

Boobies, bosom, breasts, ta-tas -- I thought I'd heard them all until a friend referred to hers as "the girls".

Gee.  Does this mean guys refer to their breasts as "the boys"?  I thought "the boys" were their nuts.

I'm so confused!