I've got a couple... and they all involve me. On my first recital, sophmore year, I was doing 2 movements of Kennan. I had this stone-lined cup I was using in the slow movement. I filed it way down. (By now, I'm sure you can guess where this is going). Well, go ahead...hum the first few notes of the slow movement (bah..dah dah wah CLUNK!). Embarassing. Fast forward a few years. First concert as principal trumpet in the wind ensemble I'm with. We're doing Prelude and Variations on Gone is my Mistris, by Sclater. There's this andante variation in 3/4, with a solo for cornet 1 then maybe 2 measures rest to get the mute in. So, I put it in my lap. Well, tux pants don't have the same gripping power as jeans do. I learned that first hand as the mute fell to the floor and produced a rather loud and resonant sounding thump on the riser.