Nipples!

I was wondering why women's nipples ranged from different kinds of sensitivity/insensitivity. I realize that it may have to do with the nerve endings, but do they have any relation to breast size? Is nipple insensitivity more dominate in large-breasted women? Why is it that men typically have less sensitivity than women? How can men/women increase their nipple sensitivity? Would this be something that you would even recommend?

You were right on the first point, nipple sensitivity pretty much has to do with nerve endings. There is no correlation between nipple sensitivity and breast size or sex/gender.

Now there may be other things going on here though. A woman with large breasts may have dated several people who loved her breasts and gave them a lot of attention. Having the same spots touched over and over can desensitize them for awhile. In this case it can be nice to teasingly avoid such areas. Nibble, suck, lick, caress, etc every other part of her breast except for her nipples. Spend more time on the rest of her body. You'll often find that if you are avoiding one spot, that spot becomes the center of attention and that is all this large breasted woman will be thinking about. "Oh god when is he/she/ze/they going to get to my nipples!?! They're aching to be touched!" And well that can just be all kinds of fun, but discuss it first with your partner.

I am especially interested in the fact that you brought up men's nipples. Men's nipples are just as sensitive as women's. They have pretty much all the same wiring there. A nipple is a nipple is a nipple. What it comes down to is that somehow we got it in our heads that nipples were only sensitive to women and god forbid a man like something that women like. That would somehow make him less of a man. The same argument is made for men liking anal play and how only gay men enjoy that. Really, sexual pleasure is not tied to any of these things. We like what we like and it isn't based on sexual orientation or sex (as long as we're using the generic term genitals anyways). So guys, get over yourselves and just enjoy the pleasure and stop asking if it makes you less of a man. It makes you more of a man to have the courage to let go and just enjoy. And hey I've known a few very muscular macho men who would take a good long nipple suck and nibble over a blow job any day. But just like women, there are also men who don't get much enjoyment out of nipple play. So if you aren't sure, ask.

There are ways to make nipples more sensitive, yes. One was the way I listed above about teasing. Another way is to have your nipples pierced. A lot of people report their nipple sensitivity increasing with pieces of metal in them. Some get increased sensitivity through nipple clamps or pumps. However, this doesn't necessarily mean that increased sensitivity feels good. It could also just feel painful. If you or your partner's nipples just aren't that sensitive, don't worry about it. I'm sure you can find other places on your bodies that elicit the response you want.