My personal favorite is rather convoluted. It takes a few minutes to tell, but for my money it's worth the punchline. You must appreciate puns to appreciate it yourself. In this case, it's a very clever pun more than worth the set up. Honest!
It has produced groans. It has produced, I swear it's true, laughter. Genuine, heartfelt laughter; and not just from me. It has also produced "You kept my attention for five minutes for that?" from a good friend. Hey, good jokes run the spectrum of reaction.
One day I'll tell it. I'll write it down right here and you can judge for yourself. Once I do, you will love me or hate me for it. It's that good of a joke.
Hopefully you're hating me right now for whetting your appetite but not telling the tale right here and now. Gosh, I hope so. If I haven't done that, then what's the point?
But I'll tell you what. I'll tell it in ten days. Is that enough to keep your attention?