I had a friend awhile back who bought a bottle of "The Source", which is 7.1 million Scoville Units. (Costs about $100 for a once oz bottle)
We would use it to add heat to the gumbo we make in 5 gallon batches. All you could stand was dipping a toothpick into it (it's about the consistency of molasses) about a quarter inch, and then stirring the tiny amount that clung to the toothpick into the pot of gumbo. We tried using a whole drop from the dropper ONCE, and it rendered the gumbo almost inedible, it was so dang hot.
It was pretty great stuff overall- added heat without changing the flavor of the gumbo like hot sauces would. But MAN, you don't DARE get any of that on your skin, or you are in for a world of hurt for a LOOOONG time.