My favorite would be in Murder Under Glass when Columbo crashes Paul Gerard's dinner party for his Japanese friend, and the guest asks him if he has a hot suspect and Columbo replies, "Oh, I've got my eye on one." and turns and looks at Gerard, who just gives a little smile back. I know it's not a great episode, but it's one of my favorite scenes in the entire series.

And of course there's the impromptu speech he gives in TRY AND CATCH ME, where he mentions that he can't help liking a lot of the murderers he meets, and he glances at Abigail.

one very entertaining one is in "Etude in black", when they're at the Hollywood Bowl. Like you say, it's veiled, but the veil is so thin it even makes the murderer laugh. Columbo says "suppose it was you?" (who killed her). Alex says "what?" Columbo says, "I'm not saying it WAS you, I'm just using you as an example". Alex laughs, and so do I.

I had forgotten about the instances where Columbo has only to knowingly look the murderer in the eye to really drive home a statement, but those are wonderful examples. They reminded me of the scene in "A Deadly State Of Mind", where Columbo is discussing the case with Dr. Collier's friends, and (if I'm recalling correctly) Columbo knowingly looks at Marc when saying something related to the perpetrator. Of course, there's also the funny part in that scene where Columbo mentions that the murderer must have been a smoker, causing Marc to quickly toss away his cigarette.

I agree, Clay, Alex's nervous laughter in "Etude" is hilarious, and a quality that I think really made that character more down-to-earth and human than a lot of the other murderers. It seems like throughout the episode he has a look of manic anxiety on his face, with an almost perpetually cock-eyed half-smile and nervously slanted eyebrows suggesting how thoroughly Columbo's frequent visits are putting him through the wringer.
Also, that line of dialog reminded me of a similarly funny exchange, with Columbo talking to Emmet Clayton in "The Most Dangerous Match": "I didn't say you WERE the murderer, I said IF you were the murderer..."

So glad you brought this topic up! There are so many, and it's often the point in the episode that I enjoy most. One of my favourite moments of him letting the murderer know he suspects them, is the scene in Blueprint for Murder in the university lecture hall. Columbo mentions the classical music in the car, then mentions to Elliott Markham that he noticed in his office that Elliot listens to classical music. But the clincher is when Columbo ends that conversation with "enjoy your dinner". Love that dialogue so much, especially because of the enjoy your dinner reference to wrap it up!

Another one might be when he asks Viveca Scott what she uses to put her beauty mark on every day.

Yes, the mention of the classical music was a great way for Columbo to sort of indicate that he was zeroing in on Markham. It's one of those clues that could just as well be tied to a large majority of the local population in general, as Markham mentions, but Columbo wastes no time in narrowing it down to Markham in particular, showing how audacious (yet spot-on) he is in his insinuations.
I hadn't noticed it before, but that "enjoy your dinner" line really is a hilarious way for Columbo to end the conversation; that could almost be another variation on the topic - the instances where Columbo says something seemingly innocuous that might actually be his way of rubbing in the fact that he's making (or starting to make) the murderer's life an unlivable nightmare.

I think it is interesting that Columbo often acts like a puppy but pretty much does as he pleases. A good example of this is the episode about the actress who owns the property in the middle of the studio. The studio owner very strongly tells Columbo not to lean on the actress or upset her, and that if he did columbo would have 'to answer' to him. Yet a few scenes later Columbo brings the actress to the police garage where she sees the burnt car her victim died in.

Another example is his encounters with Chief Halpren. There are others too.

All great examples!

In "Now You See Him," when Santini has removed handcuffs that Columbo secretly refitted with the "pickproof" lock from the murder scene: "I knew you could do it." And better than the line -- the WINK! In closeup, like from Santini's viewpoint -- priceless.

Yes, I agree with you Ted. The Santini lock picking was one of the best examples - Columbo knew Santini would have to go through with the lock picking because it would be too humiliating to have the audience think he couldn't do it, but it was definitely the defining moment to prove he was capable. That has always been another one of my favourite moments!!

I love the golf scene with Dr. Kepple. "Gee Doc, for a moment there I thought I was gonna ruin your game." "Not a chance, Lieutenant". Also, after the couple from Encino gives Riley Greenleaf an alibi, his lawyer tears into Columbo who self-deprecatingly apologizes but then innocently hits back with: "You said: "Those people", More than one. Maybe the blackout is starting to lift". He just shredded the lawyer with that.

And one of my all-time favorites is with Dr. Mayfield when he sets his desk clock. "Oh, you're being too modest Doc. Most people when they heard about a murder would be in shock, but you sat there calmly and set your desk clock."

And finally, to Mrs. Williams: We couldn't have you convicted on the wrong evidence".

I'm a little off on the dialogue but I think most people on this forum have every scene down in their memory anyway.

the scene with Riley Greenleaf and his lawyer in the driveway is classic. the way Columbo switches back and forth addressing the lawyer and then Riley, I don't know why but it was just great. And then at the end "that's probably it, his subconscious." We know that Columbo isn't buying that explanation, but Riley and the lawyer don't know what to think.

I love in Death Lends a Hand:

"I have a feeling when we find our friend...we'll see he has a bad temper" (words to that effect)

the scene where Falk and Culp are at Culps desk....where Columbo brings him the "files" personally...is one of my fave acted scenes....where Brimmer feigns appreciation for the files, claiming they will help a great deal

I have so many and I agree the main heart of the entertainment is when the interplay between the murderer and Columbo develops into the veiled accusations. The more powerful the murderer, the more aloof and self important the better. One of my favourites is when (death lends a hand) Columbo says "What a coincidence! There we were talking about left handed people and there you are left handed". I think that is a fantastic moment particularly the way he does it, with such feigned surprise! Exquisite!

The climax of "The Bye Bye Sky High I.Q. Murder Case" is a great example, where Columbo goes through just about the whole way in which the murderer covers up the crime, and then Oliver Brandt fittingly finishes it for him.

Once in a while he's talking that way to someone other than the killer. There's the LOVELY BUT LETHAL scene between him and Bruce Kirby when he says so casually "What do they call that - octagonal?"

There's one in By The Book when Columbo is at Ken's house and he notices Ken opened his mail....some where in the dialog columbo slips in the line " I know you did it" but "Could you go over where you were again".