|Don't ask what body part...|
You get a busy evening on a hot and humid day before you body has fully adjusted and it is like the Amazon rain forest in my pants (insert Anaconda joke here). And as the shift wears on, you can feel the heat building in your skin. You can feel the chafing going on, but you are busy and food needs to be run. It isn't until you sit down after your shift, be it for a bite to eat or when you hop in your car that you get the sensation that you ass crack is on fire, and perhaps it has spread to your inner thighs. I suspect guys have this problem more than ladies (we're the sweaty ones generally) but I've heard female servers complain about it too.
What can you do about it? We first good undies without irritating seams are helpful, Plus avoid cotton at all costs, in both your undies and pants if at all possible. Cotton locks the sweat against your body creating the perfect environment for jungle crotch. Under Armor is making some good stuff, but there are other brands as well.
If you feel the burn starting, in a pinch some corn starch can work wonders when applied directly to the affected area. It works better than talc. Corn starch is very fine and slippery, plus it dries the skin out a little bit. Now I don't know if there are health risks for you ladies using it on your good bits, so beware if you try it. I'd hate to see you drop a loaf of corn bread the next time you pee.
I learned of the corn starch in the military years ago, and it was a life saver. Since there was always some in the kitchen, it was a quick fix if you couldn't see the doc. Of course don't wrangle your junk and then reach back in for more - take a scoop and put it in something and go elsewhere to apply (like the bathroom Private!)
Anti-Chafing Stick. It is like a deodorant stick of magic. It comes just like your deodorant and you apply it in the very same fashion, only you apply it to areas where you have the friction. I've used this in a number of athletic applications, but now I keep a stick of it hidden at work for those emergency needs. No I won't share mine with you, I don't want whatever is crawling in your pants! But seriously, if you've ever experience this (and many servers know what I'm talking about) this stuff is heavenly. And what I really like is with one application I can make it most shifts without any further problems. I keep some at home and preemptively use it probably at least once a week depending on local weather reports and what else I've been doing that day. I also use it when I go for a run.
This stuff is a life saver.