A "shaggy dog tale" is a joke that consists of a long build up and an anti-climactic punch line, which is often a pun constructed by making changes to a common phrase or expression. I loved them when I was a kid. I don't know why I found them funny, since they're really just stupid, but I did.
I knew what the Mann Act was prior to Spitzer's downfall, for two reasons. One is a movie I loved when it first came out, "The Great White Hope." The other is a shaggy dog story whose punchline used the Mann Act. Does anyone remember the joke? All I can remember is that it ends with something about transporting something or someone "across state lions for immortal porpoises." Even that bit makes me laugh but I can't for the life of me remember the joke itself. Anyone?