Those are good ones, J and Grant, but I have to admit the first thing I thought of was the "just one more thing moment" where Columbo does NOT say "just one more thing".

It's in "Ashes to Ashes". Columbo has been bearing down on McGoohan pretty hard -- this was, I believe, in the funeral chapel or similar room -- then he turns away, walks out the door into the lobby and disappears off stage right. The camera lingers on the wide doorway. McGoohan stares after him. We see the open doorway. At this point, Columbo fans KNOW that Columbo is supposed to come back and say "just one more thing!"

Except he doesn't. Finally McGoohan, who understands the joke, calls out, "Lieutenant -- have you gone????"

"Ashes to Ashes" has a number of these inside jokes and references, put there by Pat McGoohan as easter eggs for the longtime fans.

This is a little trivia question - in which episode does the killer say the line to Columbo, not the other way around?

It would be interesting to know when he said it for the first time.

It seems, from my trusty copy of "The Columbo Phile" -- in which Mark Dawidziak collects a bunch of these quotes, in chronological order -- that the exact quote "Just one more thing" was first spake in "Lady In Waiting" (1971).

But variations of it were these from the first:

"Oh one more thing" - Prescription Murder
"There's one detail that bothers me" - Prescription Murder
"There's just one thing I'm not clear about" - Murder By The Book
"Oh, one thing I almost forgot" - Dead Weight

Also from Murder by the Book: "There is one thing, not that it makes much difference..." when Columbo asks Ken why he drove back instead of flying.

GRANT:

Just gleaning through episodes in my mind I picture Riley Greenleaf, saying One more thing to Columbo.

I cant remember it specifically but that what comes to mind... Correct?

That's one I hadn't even thought of, so I'm glad to see it here.

The one I actually meant was Abigail Mitchell.

In "Lovely But Lethal" when he leaves Viveca's studio, and she picks up the telephone to call somebody: "There's a Lt. Columbo.." and BAM, he's RIGHT there in her face, looking up through his brow at her. Fantastic.

Another one like this is in "Swan Song" when Columbo gets done questioning Tommy Brown about something and starts to leave his home. Tommy turns to answer the phone and tells someone to cancel the Tabernacle and pay everybody off to date. He hangs up, sits there for about 2 seconds only to have Columbo reveal that he never left.

Yeah, that was a classic scene ... "I knew you were stopping the project."