While out driving today during some of my final PCT shopping, I passed a car (I would later notice that it was a Mercedes) with the license plate BENZKO2.
So, naturally, my first thought was: "Ben's potassium oxide? Does potassium even rust?"
(It should be noted for the record that KO2 is actually potassium superoxide, formed by burning. Oxidizing ("rusting") potassium gives you K2O.)