You'd think they'd escort them out for that.

You should have stopped playing, faced your heckler and said, “Hey, I don’t come to where you work and knock the dick out of your mouth!” After the laughter subsides, take it from the top!

He’s wrong. You don’t suck; but now your life does

I'd invite him backstage afterwards and hide his body inside the piano once I was done.

OP, Whatever teacher, principal or other administrator was supposed to be in change of the assembly really blew that one. The disruptive heckler should have been escorted out and given detention or some other punishment. It should not require the pianist to have to take care of disruptive individuals. You are not the loser, the disruptive person was!

That’s when you stop playing, stand up and ask him to come up on stage to see if he could do better. When he says no, tell him to sit down, shut the **** up and show some god damn respect, before you jam an f sharp up his ass. Problem solved.

I would have stopped playing and call for an intermission. Then proceed to personally escort him out and give him a "lesson" in manners.

oh come on. I'm not buying this. if this was at school I find it unlikely that not one teacher or person in authority said anything.

Where the heck were the teachers/authorities? That's unacceptable.

All these people thinking an adult, or anyone, should have stepped in and loud public bullying like this cannot have happened - I can tell you from experience this absolutely happens without intervention, much of my own school life happened like this and most people didn't/don't believe me that it was allowed, and makes the person being bullied just feel that much worse... I'm very sorry this happened to you.