You do need to come up with your own spiel, but I spent about 3 minutes on the entertainment value of having the hole in the middle. Many times in the office, for example, donuts get old and stale. If they don't have holes in the middle, they aren't good for anything.
But if you visualize (insert hand motions) creative employees thinking up new solutions to new problems, you are going to want to do something creative with the objects you find laying around. Spinning donuts around one's finger is a surefire way to spark creativity.
Sure, you can do it with pastries, but employees would have to create their own holes. We don't need to encourage employees to find loopholes, only solutions.
Food deserving the title of "donut" should be noble enough to be easily played with. Ever tried making a hole in the middle of a jelly "donut" (that isn't really a donut)? That sucks.
With a donut in pure form, you know what you're getting. Who knows what they put in those "long john" pastries? You don't know where that's been!
I had 3 points, all of which started with "e", this one was entertainment and was the easiest to do, hence it took the longest.
Oh, and by the way, I was being punished, and I'm not sure the teacher meant that I was supposed to actually deliver this speech, but the words came out of his mouth so I thought I should take the opportunity to waste class time.
Good luck. And you could probably make a funnier speech on "101 MORAL applications of the banana." If you need more ideas, don't hesitate to let me know. I've had to deliver speeches on everything from "why firetrucks are red" to "postmodernism in the 90's".
If you're looking for an easy speech, you can do one on girls. Unless there's some sort of class vote and the girls outnumber you, but it could still be an easy speech. I've done one on PC's vs Macs a few times, and I always made it incredibly biased one way or the other just for fun.
If you're trying to appear "SMARTS," you'll probably want to prepare. I never did, it always made it seem less real and I turned out to deliver speeches that weren't shooting straight from the hip or the heart, which for me are about the same thing.
Oh yeah, and one of the most fun persuasive speeches I've given (next to the adolescent's right to privacy over the parental right to know) was why the earth is really flat. Usually with these speeches, at least on the high school level, they're looking more for quality of presentation than quality of content, but it might be different if they're requiring things like notecards, journals, and actual preparation time, which I rarely bothered to do after my freshman year (of high school, not college).