@Tailbonecracker
I do this, too. I refer to this as "cracking my butt". It's very satisfying. It usually happens when I'm sitting at my desk at work. I slouch down, stretch my legs out, and squeeze my butt. I do sometimes, like some other joints as well, get the feeling that it needs to crack, but can't quite get it done. I don't think I've ever felt pain in this crack, though.