Why does one of my nipples go in? And take a lot longer to get hard than the other one?
Some girl have what you call inverted nipples. It's normal even though not everyone has one. Don't worry about it.
EDIT: I forgot to add, if this is something has has recently started you want to get it checked out by a doctor, then it could be a sign of a underlying problem.
hmm I've never heard of anything like this but it doesnt sound much of a problem but I would advice you to go to see your doctor if no more advice is put forward :)
It's normal, just a little bit different. If you really care, you can see a plastic surgeon and have it changed, but there's really no reason to.