This is an old joke, in which every word starts with the same letter.
Philologists and literary enthusiasts often cite it as an entertaining example of alliteration. Nobody is quite sure where it came from, but one popular theory is that an Pater gave a pupil detention on account of misbehaviour, and as punishment made him write an essay where all the words started with the same letter. The pupil made up a story about the teacher himself. Regardless of the fact that the story was somewhat obscene, the pupil completed the task, and was forgiven.