Well done, Murcheson!! You beat me to the post by just a short while -- I just got done watching it, as I was pretty sure this was one of the few episodes with an actual "joke."

To back up and give the context, this was a joke that the victim, Frank Staplin, had just faxed to his wife in Hawaii right before his supposed suicide -- Columbo is confronting Finch about the incongruity of Staplin allegedly killing himself in the middle of faxing 2 jokes to his wife. Columbo tells him Staplin's "Jewish joke," instead of the "Irish one." And it's just as you said.

Finch doubles over, laughing immoderately to cover his quick exit.

Maybe funnier than the joke, to us today, is Columbo's earlier amazement at the huge "facsimile" machine in Staplin's office (in 1990). "Isn't that remarkable," he marvels. "A letter sent 2,500 miles across the Pacific in 14 seconds!"

I might recommend this episode to anyone who still thinks that all of the ABC movies were terrible.

The episode was called "Agenda for Murder", where Lt. Columbo tells the following joke to the suspect:

"There was this Jewish lady walking down Beverly Drive, and coming the other way, this flasher guy in his overcoat. When he gets up to her, he whips open the coat. She looks at him and says, 'You call that a lining?'"