It doesn’t necessarily have to be a professor if you think it would be appropriate for a university setting.
Don’t. Just teach.
I had an interesting one once:
We were paired up with the random new person next to us. Interview each other. Then, everyone gets to introduce their interview partner to the rest of the group.
First year undergrad math : “Forget everything about how you did math in high school, that’s not real math. Now let’s start from the basics with an intro fo proofs.”
My highschool chem teacher’s first words were. “Ice breakers are so boring, let’s go blow stuff up!” And then imediately showed us what happened when you drop a cube of pure sodium on water.
Best fucking class I ever had.
Eberybody stand up. Those who can answer a question can sit down (this was the first class of the subject in the semester). Those who can’t answer can either remain standing or leave the class and drop the subject. It surely broke the ice, especially since the organic chem subject was compulsory.