I did a good one on myself a while back. It was the Boy Scouts' District Camporee and I'd just woken up and, by definition, required coffee. I got out the propane stove and began setting it up. Unfortunately, I didn't realize the propane hose was pressurized and it let out a blast of propane from the fitting. Now, the day was going to warm up but mornings are still cool here in the desert. And, actually, the depressurizing jet of gas alone was cold enough to cause frostbite. So that's what it did; right across the back of my right index finger. What did I do? Grabbed it with my left hand to finish tightening down the fitting. And now I had frostbite across the back of my left index finger, too.
Warning, the following section includes graphic pictures of injury.