For me the most embarrassing thing that can happen to you during an experiment is for it not to work! I once was presenting a concept to a room full of people (including some press) and the technology I had been working on just didn’t work. I couldn’t explain it. They were all really confused, and I was very embarrassed. I discovered later on that the batteries I was using had died. Lesson = always check the batteries before a presentation! There is a classic example of that happening at this launch of a technology that was meant to slow down a car by itself in traffic (and stop it crashing)… the batteries had died though, and the car crashed! http://www.youtube.com/watch?v=H9_ePZWxWGw
We often do experiments, in the dark, which use warm salty water (just like our blood plasma) to keep cells alive. One frustrating day, after I had spent a lot of time staring down the microscope, I turned on the light to find that the salty water had leaked and flooded the base of an expensive microscope filled with electronics. It wasn’t much fun having to explain that to the “boss”, particularly as I had to do it with wet pants!