Not bad overall. You've told the story, and developed the gag from build-up to punchline. The art style was consistent and animation fluid. Audio sync'ed up, so quality isn't an issue.
In comedy, there's also the matter (at the punchline stage) of "follow through". The punchline here is a visual proof of Prof. kukui being a psycho. From that (in the description) and Moon's reaction to the demo', we could get that the poor creature being used was likely destroyed by the crash. The "follow through" that should send this idea home would be one of two things.
1. Swap of camera view to the crash sight on impact, showing lots of destruction, fire, blood, gutts, spit and ass flying everywhere... big mess. ...and you could include Moon's sobbing, shrieking, or swearing in the background...
2. Hold the view on the two of them watching this thing to fruition and crash... slight pause (neighborhood of a second and change) and rain splatter from the mess down on them both as he beams proudly over his lesson and she goes through all the facial expressions and voice work of shock, grief, and some nausea while blood and gore speckle over her face and some entrails end up tangled in her hair.
So the conclusion is an almost complete sight gag. The joke is told, but only just... and it "feels" a little rushed. This is the unfortunate business about animation. It's hard to stick to it and take the time to get everything quite perfect. It doesn't really matter what joke or gag you're working on, but that follow through is the part that really separates an animator from a kid with a passing interest and a wacom pad.
On audio... It's possible that it was only my connection, but it seemed like the ending credits and theme seemed to suddenly (inexplicably) jack the volume way up. I only point it out because on the chance it got uploaded that way, you would definitely be well advised to double check your audio and volume controls on output before exporting or uploading. Even just give it another viewing yourself to be sure... "Good audio can make you, but bad audio will break you." -cinefix- (youtube)
Okay, as I pointed out, it was pretty good overall. So don't forget to breathe, relax, and keep on keeping on. I really do mean these suggestions to help you. :o)