The Pizza Trio

Pedophilia, Incest, and Zoophilia (P-I-Z, hence the word Pizza). Often used in comparison to something deemed abhorrent.

Cyan: Did you hear that the teachers at a nearby school have been giving children pornographic books to read?
Sky: Yup. And with all of the kinks mentioned in them, it seems like they're intent on teaching kids about everything shy of The Pizza Trio.
Cyan: Absolutely disgusting. Kids should not be taught these things.