Oh wow, do I have some good ones. When I was in 7th grade I got a metal washer stuck on my finger during class. Because of that, I ended up spending an hour in the nurse's office while she tried to use grease to remove it. That didn't work so my mother came and got me and took me to the fire station, thinking they had a saw to remove it. The firemen, however, were not there so my mother and I went to the emergency room to get it off where they used a ring saw to remove it, after using local anesthesia to numb my hand. I almost lost my left ring finger that day, so I could have ended up being called "Jeff of the Nine Fingers".
For another fail, one summer my dad took me to work with him so I could work in retail. So one day I found a button, similar in appearance to a doorbell. I asked my coworkers several times what it did, but none of them responded. So I pushed it. Nothing happened, so I pushed it again. Same response, so I got bored and went somewhere else. About twenty minutes later, an armed police officer showed up. Turns out I had pressed the "hold-up" (as in an armed robbery) button. The company lost 100$ that day, and my dad ceased bringing me to work with him.
I'll share some more as I remember them.