How is it possible that Catullus, one of the most unabashedly bawdy writers, is taught in AP Latin?

Answer 1

He isn't anymore. He was one component of the AP Latin literature test, but it was discontinued in 2009. When he was part of the curriculum, they managed to come up with about 800 lines' worth of his poetry while keeping it fairly clean. You can find a list of the required readings here:

https://en.wikipedia.org/wiki/AP_Latin_Literature

You will note that poem 16, e.g., is absent from the list.