I was a sophomore in high school and working on "Romeo and Juliet." I was both the ASM and Friar Laurence.
About a week before we opened, we were installing our set and setting everything up for our tech and dress rehearsals. For this, we had some large ivy vines that had to be cut down to the right size, and my drama teacher had graciously allowed me to use his Swiss Army Knife to that end.
I cut a few vines and took them over to the set piece that they would be stapled to so that I could make sure they were the right length. To do this I needed both hands, and so I set down the knife.
I walk back to the table with the full vines to find the knife gone. Then, a few seconds later, I felt the sharp press of a fine point in my back just about where my right kidney is. I tense up, and then whirl around to my left, knocking the arm away from my body with my left arm as I complete the 180-degree turn to face my would-be attacker. I find myself face-to-face with a freshman in the class who thought it would be real funny to pretend like he was going to stab me in the back.
Five minutes of chasing him around the room, followed by approx. one minute of holding him against the wall by his throat and threatening to beat the crap out of him, and the situation never happened again, although said actor stayed in the class and continued to annoy the hell out of me for the next year and a half.