We had a similar incident!
but we knew who did it and why.
See our super cool awesome band teacher quit because his wife almost died cuz she got in a car crash while she was pregnant it was really sad! >:[
So we got this nasty 90 year old band substitute teacher to teach us!
He was horrible! He'd make us run track every day with instruments we did'nt even play and he kept bringing out his Tuba and shouting at everyone saying "Tuba is the only real instrument, all other instruments just support the Tuba bla ba bla"
Every football game he'd bring it with him and show off.
So while he was getting food a couple of the drummers replaced his Tuba with a Flute (he hated the Flutes worst of all) and hid his Tuba somewhere.
When he opened his case and took out the flute he looked mortified.
A few months later during class some students noticed a hole in the ceiling that was tastefully hidden with a blanket and some duck tape!
In that hole the janitor found a brass Tuba separated into about 65 pieces lol He gave it to our band teacher in a brown paper bag! XD
The guy quit soon after that!
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im a tuba and at a football game were put right infront of the drums which are in the very top. right when we were getting our stuff together to exit i picked up my tuba and my mouthpeice fell out. it clunked down all the way to the major who handed it to the tuba leader. she was amazed to find that the mouth peice and bits that apparently fell with it were unharmed. she still gave me hell 
