I know how mine gets irritated - sit-ups. I just have no padding there at all (in deference to the rest of my well-padded body), and the situps cause the skin to be crushed between the bones of my pelvis/coccyx and the floor/mat/pad/towel. Bruising and abrasions ensue.
During Boxercise, when we are expected to do situps on the wooden dance hall floor, I have to go find a pad as it is too painful otherwise - with the pad it just hurts.
So, I sympathise with the OP.
Si
Wait, coin slot means ass-crack now? Man, am I behind.
stop inserting coins in it, for a start.
So what’s a coin purse then? I’m really confused now.
Gold Bond medicated. Or if you suspect you have a fungal infection you better go with something that cures jock itch.
WD40 and other lubricants tend to attract dirt. Any engineer would tell you to clean the relevant parts in kerosene and then apply powdered graphite.
A&D ointment, if we’re talking about asshole irritation. It’s gentle enough for babies, and it soothes and heals chapped skin and mucous membrane.
Is there a problem so obscure that there isn’t someone already trying to make a buck of solving it?
BaneSidhe, which is your recommendation? The link you posted, or your signature? If the first doesn’t work, try the second? 
First, the juxtaposition of this topic and sig line made me spit bagel. Nicely done, Bane Sidhe.
<mod>
Sleeps With Butterflies, that’s not acceptable outside of the Pit. Take it there if you wish to insinuate such things.
</mod>
Go with the tagless briefs.
blargh
I noticed this during yoga. There are 2 things I do to minimize the grinding (ouch!). One is to train that tailbone to kind of ‘tuck under’. It takes a little practice, but what you want is to minimize that inward ‘bow’ of your lower back which is making the tailbone poke outward. The other thing is, when on the mat, before doing situps or similar exercises, kind of wallow around with your butt so that you situate the tailbone between the butt muscles. That way, they bear more of the weight/force. If you need better butt muscles, I recommend lunges.
Wash well with lye soap; dry with slick catalog pages. Apply copious amounts of alcohol and cover said slot with large adhesive pads. Place mass quantities of duct tape over adhesive pads. Take two aspirin and don’t bother calling every again.
I recommend applying some Vaseline Intensive Care.
Unfortunately, with the weather getting colder, the relative humidity in the air goes down, and it dries everything out. You know, the whole Juneau effect.
Exactly.
It is lots of gym work (including lunges) and running that has caused contraction of said glutes to the point that I am really flat in the arse. Sitting for long periods actually hurts because I compress my glutes against my pelvis. I used to be able to drive for hours (7-8 hours sometimes) - now I need to stop after a couple. When I lie back, I either rest on the tips of my pelvis or my coccyx. It looks pretty good, just useless for sit-ups.
I watched an early Jean-Claude VanDamme movie the other day (Kickboxer) on TV - I couldn’t quite believe the roundness of his backside (not in that way, either). Mine just does not do that, and it gets heaps of working out. I want to get these sit-ups beaten, though, so I will just suffer. A flat belly to go with the flat butt is worth the pain 
Si
Spray it with Windex.
Witch hazel. Tucks medicated pads are soaked with witch hazel, chiefly. Buy a container and use them. This presupposes that you are performing adequate daily hygiene in that area.