Well, I've had a few, and I've probably reported this one on here before, but back in my orchestral days, I played timpani: we didn't have the more modern pedal timps but tuned by hand, which included using an adjustable spanner on the tap nearest you.
Right in one of the quietest, most beautiful parts of the symphony, I reached for my spanner....and dropped it! Now, you'd think a lump of heavy metal like that would hit the floor and stay there, but somehow it managed to bounce - three times, on each step down off the stage into the audience. I just wanted the floor to open up and take me away!The conductor's face was a picture!
It's over 50 years ago now, but still haunts me!