My dad told me he was going to tell me a joke about a pizza.

This joke operates on the classic humor mechanism of wordplay, specifically a pun. The brilliance lies in the double meaning of the word "cheesy." On one hand, a joke about pizza is almost guaranteed to involve cheese, making the literal interpretation of "too cheesy" perfectly logical in the context of the food. On the other hand, "cheesy" is a widely understood slang term for something that is corny, unoriginal, or trying too hard to be funny. This dual interpretation creates the unexpected twist that delivers the humor.

The real-world context of this joke is deeply rooted in both popular culture and language. Pizza, a beloved food worldwide, is intrinsically linked with cheese. The derogatory slang meaning of "cheesy" for something "cheap, inferior" or "hackneyed and obviously sentimental" has been attested since the late 19th century in U.S. student slang, and possibly as an ironic reversal of an earlier British slang meaning of "fine, showy". This joke also perfectly embodies the "dad joke" category – a genre of humor known for its often groan-inducing puns and innocent, predictable punchlines, which have roots dating back to ancient civilizations and became popular in the 20th century with comedians like Bob Hope. The term "dad joke" itself gained popularity in the late 1980s.

The humor comes from the swift mental shift required to understand both meanings simultaneously, appreciating the cleverness of the setup leading to the unexpected, yet perfectly fitting, punchline. It's a simple, family-friendly joke that, like many dad jokes, is designed to elicit a playful groan rather than a roaring laugh, celebrating the endearing "cheesiness" it describes.