Classical gig disaster: I was playing timpani, and used to use an adjustable spanner for tuning the one tensioning nut that didn't have a turnable tap on it. Right in one of the quietest and most lyrical bits of the piece, I dropped that spanner: it didn't just land on the floor but bounced down into the audience with a horrible clatter! The conductor's eyes were casting murderous looks in my direction and I just wanted the earth to open up.

And during a production of "The Mikado", the director decided it would be fun to have Koko arrive on stage on a skateboard. He successfully jumped off it, but the skateboard carried on into the orchestra pit, narrowly missing the oboeist!