It's actually quite tempting to find some sort of rubber peacock head and glue it onto a fuel separator on a random bus. Nobody would see it for quite some time, of course, and the guy who did might not get the gag. But if he did, I would imagine his reaction would be priceless. And just knowing that I set such a time-bomb for someone would be quite gratifying...
I used to be a high-school science teacher. Can you tell?