How cool! I bought a copy of "Rationale of the Dirty Joke" years and years ago (probably in the early 70s or thereabouts), and still have it. While I haven't read it lately (that may soon change), mostly I just skip over the "rationale" parts and focus on the dirty jokes, which are, for the most part, a bloody riot. One particular fave (punchline only): "If your mother were here, we could've saved the horse and wagon, too." (The rest of the joke can be furnished upon request, but to give you an idea of where it's coming from, it's in a chapter focusing on oversized genitalia.)

Laugh on, mates...

Poobs