I've never had more than a joke I've told friends passed off as someone else's work. (That is, I told the joke, they passed it around as their own.) I don't feel too strongly about humor being passed around.

I feel much more strongly about non-humor intellectual property.

I personally would have gone back to the Dean, first. Explained the situation. If the Dean believed you once, they'd probably believe you a second time.

After that, I suspect I may have figured some elaborate revenge. As you said, it wasn't super-useful. Probably nothing more than setting the professor's car on fire would satisfy my need for revenge in the matter.

Had it been more valuable, I probably would have attempted to kill the professor.

You can steal my money and my car and my house and my lovers and food and coffee; but when you start stealing my thoughts, you've gone just one step too far.