Stimulate it.
No
That you decided to get a nipple piercing.
You're going through puberty.Dont worry it's normal for this to happen.I've had that happen to me.
yes they will be hard
Your eather horny or cold!
A long breast with no nipple.
If you mean that they are always erect it is normal and nothing wrong with you.
Increased of blood flow so when you are cold or excited
You get cold, or stimulate them mentally or physically.
Guys LOVE Hard Nipples. It Is Easier For Them To Suck On And Wrap Their Tongues Around!
About as harmful as getting a hard nipple.