A "turd cake" is a useless little nerd, most often they are in their early teens, like 12 year old boys.
BUT, they can also be adults who never grew out of the "turd cake" stage.
ex: Mr. Charles, can I have this? Mr. Charles, can I have that?
Mr. Charles, I am cooler than you.
Turd Cake Repellent starts with: No you useless "turd cakes" stfu, and go bother your parents.