Pie plates are those plastic or metal discs that come on many bicycles, and are also called spoke protectors.
They supposedly guard your spokes against chain damage if it ends up way up there. The truth, however, is that any properly tuned bicycle would never need one thanks to the limiting screws on any modern derailleur.
I commute on a fixed gear bicycle (one gear only, no coasting, no derailleur), so in my case a pie plate would be extra super duper useless. Perhaps this was why I was subjected to my harrowing meeting with Inspector Goose:
Those three quick steps still cause me to shudder with fear when I see them. Most of you have pie plates on your bicycles. I have no personal interest in your removing them, but beware Inspector Goose, man, beware Inspector Goose.