Back before I was diagnosed with Celiac Disease, every time I ate something I'd have diarrhea 2-3 times about 30-45 minutes after I began eating. This is no normal diarrhea, this was stomach acid pouring out of my ass diarrhea. I lost 15-20lbs simply because the food I ate was passing through me so quickly, my body couldn't absorb any of it. The only painful thing was the knowledge that I'd be on the toilet in half an hour if I wanted to eat something. Kind of sucked.
Now to the most painful thing:
Last summer I was working in a concrete/soil testing lab. It was my job to test the compressive strength of the various samples from concrete pours throughout the city. We also tested grout and mortar. To test the concrete cylinders (4" dia, 8" tall), we put steel caps with rubber pads on the top and bottom to make sure the pressure was distributed evenly. Testing the grout was a PITA. They were 3.25 x 3.25 x 6. We had to cut off the top and bottom with a masonry saw because they were made in cardboard molds (as opposed to the plastic molds the concrete cylinders were made in). After the top and bottom were cut off, we had to cap the grout prism with a sulfur-silicon compound. This shit stank up the entire lab for hours as it had to be kept at 400F.
Anyway, you pour the capping compound into a small mold and then place the grout prism in the mold and viola, in 5 minutes you have a capped prism. Well, I had 1 prism that was smaller than normal; the person who made it screwed up and I had to cut off more than normal to get a good edge to place it in the mold. I poured the compound into the mold and then placed the short prism into the mold. Along with my pinky. I don't think I've reacted faster in my entire life. Holy crap. I immediately poured cold water on it but the damage was already done; I had a huge blister on half of the length of the left side of my left pinky. This hurt enough that I think I went into shock, I started shaking, I had cold sweats, and I was nauseous.
However, by the next day, it was completely painless.
Completely irrelevant to the topic:
Those grout prisms were a huge PITA. Preparing the cylinders for testing took ~10 seconds/each to get it out of the mold. The prisms took about 15 minutes each. Burning my finger because of them only solidified my hate.