OK, I'll bite, at the risk of stepping into something. I'll try, at the risk of potentially failing, to provide something perhaps more concrete (and maybe more to the point of the original post). It seems perhaps important here to try to answer the original post, and in actionable terms, rather than argue around each other. Maybe the question can inspire, rather than open up a bunch of silly flaming?
I would perform of one of two not-yet-famous tricks, either the Failed Needled Balloon or the Muffin Through Brick That Doesn't Work Either.
Per classical Needled Balloon, I had carefully sharpened my needle. I had carefully oiled it. I had carefully bought a batch of brand new balloons and carefully tested them to be sure my needle adequately pierced the balloon without popping it. I had inserted confetti into the balloon.
I stood confidently before the audience. I showed them, oh so carefully, that terribly sharp needle. I showed them just how sharp it was by touching my finger tip to it, oh-so-carefully. And they were convinced it was sharp. Then, with all the bravado I could muster, I showed them a balloon, and inflated it. It was a brave, strong, bold, and true balloon, a true inspiration, and a pity it might die. As I inflated it, the confetti swirled dramatically inside the balloon, a herald to its bravery.
Now, dramatically, I oh-so-carefully inched the point of the needle toward the balloon. I kept fearfully looking away, trying with all my might to go through with the oh-so-frightening act of actually touching the balloon with the needle. Everybody was terrified with me that I might actually touch that balloon, and that it was going to pop.
But I *knew* inside myself that this was going to work.
So, I proceeded to touch the needle to the spot on the balloon where I knew the needle would penetrate the balloon, where I knew without-a-shadow-of-a-doubt that it would work because I had prepared it relentlessly. And I knew, for absolute surety, that in a short moment I would be showing so dramatically and so proudly that the balloon was, of a surety, impervious to the terrible, sharp weapon.
And the balloon popped. It echoed throughout the hall.
Confetti flew everywhere. And I stood there dumbfounded. I was prepared to continue going through all the remaining motions, to push the needle through the other side, then pull it completely through, then pop the balloon through the side and take my oh so triumphant bow. But it had failed. It wasn't supposed to do that. I stood there, completely shocked that it didn't work. And I had been so intent on what to do next that I had no idea what to do next now that it didn't work, so I stood there dumbly with a look of complete and utter shock on my face.
It brought down the house. After perhaps 30 seconds of dead silence, they laughed. For minutes, they laughed out loud, helplessly. Then I got a standing ovation.
We can go analyze it, in terms of reversal of expectations, or in whatever terms you want, but quite simply, the completely unexpected look of shock on my face, after I attempted to do something so completely ludicrously stupid (so much so that I myself had been acting up to increase the proof of how ludicrous it was) was, apparently, quite funny.
Stupidly, I tried the trick over again later, and it actually worked as expected, but didn't do much for the audience. Just wasn't the same.
I offer the Muffin Through Brick That Doesn't Work Either: a similar attempt to make a muffin penetrate a brick, trying to convince us all along that it's going to work, while we're not really sure, and we really can't bear to watch and here goes nothing and then SPLAT it fails, throwing chunks and crumbs of muffin everywhere and the poor sap magician is actually shocked that it didn't work.
Sort of the classic sucker trick involving "get the magician up a tree, throw rocks at him, then get him out of the tree", only I stopped at the first rock. And stood there dumbfounded. (Getting him out of the tree was a waste of time -- it didn't work).
If that doesn't work for you, I'd try for something that touched the child in all of us -- something that inspires wonder. Where I can be one more of the children seeing something for the first time, hopelessly lost in the fun of a completely new experience. Don't yet know what the particular effect would be -- can anybody help with it? I'm thinking maybe a snowfall inside a theater, so real it feels cold, it gracefully lays tiny, dainty snowflakes on our hands and faces, touching everybody, then it disappears without a trace, to a dry, warm theater.
Perhaps defining ENTERTAINMENT (writ large) is like trying to define pornography. Story goes, a famous judge was struggling with creating an objective definition of it (naked people? art has naked people. Intent to tittilate? How do you prove intent? Crass? how to define? and so forth). The working definition of pornography, based on his decision, is that he "knows it when he sees it". Suitable for a courtroom. But if you want to teach it, you might have to show an example or two.