When I was an undergraduate, someone presented to me a proof of the Fundamental Theorem of Calculus using entirely vegetables. I found this incredibly fun at the time, but I can't remember who presented it to me and my internet searching has not been successful.
The proof involved pinning various vegetables to a board and using their locations as variable names. I hope to find a reference for this -- obviously it's a bit of a longshot.
I was at the University of Michigan and it probably happened around 2004. But I have no reason to believe it was invented at that location or that time.