I can't narrow it down to just one, but while I have watched all 69 episodes at least twice, and own them all on DVD, I will never again watch:

Murder in Malibu - Terrible acting and I can't stand Wayne Jennings and the sister Jess

No Time to Die - I hate it like everyone else

Last Salute to the Commodore - T'isn't is the clue? You gotta be kidding me

Old Fashioned murder - I find the characters very bland and uninteresting

Bird in the Hand - Not everyone agrees, but I really don't like Tyne Daly.

I have a problem with any later episode where a partner of Columbo's uses handcuffs ("Night Life") or fires a gun (I can never think which one has that moment) or goes into that snarling "tough cop" mode in general. The only partners he should ever have are low-key "Sgt. Kramer" types!
That includes the ending of "Goes To College." No matter how much other people love seeing "those young punks" led away in handcuffs by Columbo's tough cop partner - "Come on, you!!" - that just isn't "canon" for me!

When it comes to the original series, one of my least favorite ones is "A Deadly State of Mind." No matter how good George Hamilton and the others are, it's just kind of "okay" to me.

I have one single problem with "Identity Crisis," and that's that the spy story sub-plot confuses me completely. That shouldn't interfere with my liking it, but it does a little.

Mmm, in no time to die, which I re-watched recently, there's a few columbo colleagues who enter the room the kidnapper is in in the end with a pistol, including columbo, and his nephew, who is also part of the police, shoots the kidnapper 4 times, I'm guessing it counts as what you mentioned.

There was also murder of a rockstar episode, where a female sargeant tries to shoot the victim's bf when he's running away, after noticing the police is after him.

Maybe from the most hated ones:

- "No time to die" and "undercover" - I don't even count it, because for me it is just not "Columbo" but some other movies with guy who resembles columbo a little with his face. No No, and one more time No. I watched every episode around 20, 30 or 40 times (really don't know how many) but these are the only ones I always skip and don't feel sorry about it

So maybe first ones from New Series since there are more worse ones:

- "Murder, A Self Portrait" - I don't like ANYTHING about it except of nice filming location, nice weather and Vito Scotti. I just hate it. One of most irritating murderers, completely unrealistic idea uf guy living with 3 women at a time and they are all more or less ok with it. This dinner scene it top of ridiculous. Plus dreams? No kidding.. what a mess, how far fetched, and how much not "Columbo style"
- "Murder in Malibu" - senseless plot, very weak acting, especially Wayne Jennings. You just can't stand watching this guy any time he appears on screen. Columbo himself acting rather strange
- "A Bird in The Hand" - I watched it maybe 3 times only... that explains everything
- "Murder of a rock star" - not entirely bad, but there is something I just don't like. And the final clue is very weak (not to mention - how somebody can drive a car in such a mask? without holes for eyes to see what is going on on the road?? especially while exceeding the speed??)

The "Classic Era":

- Last Salute for the Commodore - I just think the same as everybody else here. But as Vito Scotti mentioned above - I still watch it because I watch all of them from first to last and always try to look for some new things for me there
- The conspirators - just hate it as well. Not that much as before, but still, I force myself to watch it
- Identity Crisis - They just went too far with this "spy" thing. Overcombined (if such a word exists in english :P)
- Most Dangerous Match - just don't like the plot and last clue, and the murderer
- Mind over Mayhem - just stupid, murderer not charismatic at all, final clue weak