I have two...
1)
My sister once tried lighting our gas BBQ. She lit the gas vent closest to her first, but the flames were so hot that she couldn't put her arm over it to light the innermost one. While she as trying, the gas reached the first vent, and a huge ball of fire burned off 1/3 of the hair on her head. Once I found out that she was OK, I LOL'ed. To this day, it ranks as one of the funniest facial expressions I've ever seen. No eyebrows = Win!
2)
During cooking class at school, my group made a stew. I forget which kind it was, but nevermind that. Seeing as it was a group effort, I was set to chopping vegetables, and thus I didn't really have any fault in how the monstrous thing ended up tasting. Anyways, the idea was that every group made a meal, and the teacher would sample them all and grade them based on the result in addition to efforts made in the kitchen in general. It was the most disgusting thing I've ever tasted, so after we'd filled our own plates, we tossed the rest of it out of the window, and told the teacher that we'd eaten it all up before she came around to our group to taste it. The window faced a forested area that no one really went to anyways, so we figured it'd be safe. Let's just say that everything went according to plan until a teacher came up from the floor below, telling our teacher how something brown and disgusting had hit an open window in their classroom.