For the same reasons as a males nipples go hard it is the result of increased circulation of blood.
it's called arousal. google it.
Because your horny
Because it is genetic, ony ten percent of girls have inverted or nipples that face in whereas the other ninety percent have nipples that go outward
It is just their bodies response to stimulus such as arousal or temperature change. Men's nipples can do the same thing it is just not as obvious.
Ice...or cold objects
so there nipples go hard
Your nipples go hard.
they go hard and you blow your load.
dont question it.....just go with it
Don't question it, just go with it
nipples nipples perverts!!!!!!!!!!!!! u guys or girls need help... go take ur meds... retards!!!!