Nipples

[Blah56]

Ok so when I was swimming recently I notice that my friends nipples were hard all the time but mine are only hard when I am cold so your nipples get hard through puberty or is it just because he is skinny and I used to be chunky

[IAMWILL]

As you develop more, the pectoral muscles (man boobs) become larger and more pronounced, which makes someone's pex feel firmer. Also, the nipple itself becomes darker and firmer as you age. Weather does play a big effect on the hardness though, so it could have just been that he was cold at the time.

[Jupiter]

Yes, in whether, your nipples could get hard if they sense a lower temperature. I really have no idea why it happens, but it does when you're swimming or outside when it's cold, or etc.

[jack_aus]

Mine generally get harder when it's colder or if they're really stimulated ;)