Sure, there's no downside to appealing the denial of benefits. But then again, I wouldn't have serious hopes of winning, because I frankly can't quite see a positive way of spinning what you did. In order to keep you from drawing unemployment benefits, the employer has to show, and because they fired you, the burden of proof is on them to do it, that you were terminated for a valid, misconduct reason. That you were aware of what the rules were, had received training and then prior warnings related to your inappropriate conduct, and that you had willfully disregarded those warnings and chosen to do something that you were pretty sure was going to get you fired.
Okay, how could we spin this to make it seem like cutting donuts with the forklift was a good idea, or a defensible thing to do? Were you on the work floor when you were doing this? During work hours? Around material and machinery and other workers? Was there a general rule forbidding "horseplay" with the machinery? Had you received safety training on the forklift? Were your other warnings related specifically to misuse of the forklift, or were they for things like not wearing your hearing protection or disregarding a policy of some other type? Your possible argument of "under a moment of great stress I was unable to judge properly" certainly could use more development. You were under a moment of great stress (as in you were being rushed, your forklift was about to crash into something, you had just worked fifteen hours without a break?) and were unable to judge properly. Judge what? Whether you were about to cut a donut, whether it would be a good idea to goof off, or maybe how hard you had turned the forklift, causing an involuntary donut?
All in all, there's no point in cancelling the hearing, they're not going to do anything but go through the process. But you have nothing to lose but a few minutes of your time. If you can think of any way why you could explain what you did so that it doesn't sound like you voluntarily and with full knowledge that it was a bad thing to do, chose to do something that would probably cause you to get fired (if you were caught doing it) then you may have a chance to prevail.
Don't feel bad, though, people have done some really crazy dumb things to get fired (like the guy who set the building on fire so he could leave work early.) But like I say, there's no downside to going through it.