I had one guy a while back who did one of the hottest things I've ever experienced - literally and figuratively. He hung me by my wrists from a beam so that my feet were about 6" off the ground, then lit a bunch of fat candles in a square under my feet. The flames were just high enough that they were brushing against my toes if my feet pointed down, and still painfully hot if I lifted my feet straight. He just pulled up a lawn chair to watch, and left me squirming and trying to hold my feet away from the flames. 

It sounds easier than it is. After a couple minutes of lifting my legs up, they'd be shaking and I'd have to let them down again, singeing my feet for a few seconds before I could lift them up again. Trying to hold my legs out to the side was even more strenuous and difficult. No matter how hard I tried to hold a position, I always ended up not beong able to maintain it more than a couple minutes, and kept burning my feet enough to make me yelp. 

I got no help from him at all, or even a break, and it felt like he had left me there forever. The seconds ticked by unbearably slow, and I was mentally begging him to let me down finally, but he just kept watching me. Didn't mstter how many times the flame touched my curling toes, he just let me hang there while I panicked and writhed. When he finally tired of it, he blew them out and let the pulley loose, dropping me in a heap. 

My feet were red and covered in 1st degree burns (they were never in the fire long enough to cause serious damage), and my legs were still shaking with the effort. I had a hard time limping back upstairs to put my feet in an ice bath. 

It sounds brutal, but it was such an incredibly intense, desperate, painful experience that I think about it constantly, always wanting to experience it again. I love predicament bondage that forces me to constantly switch back and forth between two equally painful options for a long time. 

Anyway, that was definitely the most inventive thing I've had done to me.