My worst tech accident had to be when I was setting a piece of scenery into it's fitting slot (so that it could be easily taken in and out during performances) my foot somehow got caught underneath and was locked in place in the slot under the set piece. My toes were black and blue there for awhile!
Steel toed boots are wonderful things.
My most recent injury is one I can't pin down to a single incident. All the years of wiring sets, hanging lights, and otherwise doing assembly and maintenance work has resulted in tendonitis in my right wrist. It's moderately painful, but more of a nuisance than anything else. As long as it remains at nuisance level and doesn't get any worse, I'm supposed to wear a wrist brace when I work. According to my doctor, even when my wrist is done healing, I need to wear the brace when I'm doing any kind of assembly work to prevent a reoccurrence of the tendonitis.