You have several nipple nerves that respond to stimuli whether physical or psychological. Nevertheless, you don’t have to worry because random nipple hardness is normal. They can hit full lights while waiting for a bus to work, while in the mall, or even in your home while napping.
Other times, they just go hard. However, there is a reason for every erect nipple situation, which goes back to a particular nerve whose work is to generate nipple erections. They become erect when someone turns you on and will stick out when you are cold. Regardless of how you look at your nipples, they are both weird and wonderful.
