These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Alternate Character Interpretation: Prominent ones include the theory that Columbo's oft-mentioned but never-seen wife doesn't actually exist — along with a host of other relatives that turn up in his conversations with perps — and that his "fašade" of foolishness really isn't a fašade at all.
His wife exists — there's an episode where they're on a cruise together. Another ends with them talking on the phone.
The one episode which involved the ex-wife of one of Columbo's past arrests trying to murder his wife in revenge.
Complete Monster: While a few Columbo killers were obviously and openly selfish and regarded their victims as more than annoyances, the only criminal to fit this would be Rudy Strasse (who ironically never actually kills anyone) from "No Time To Die". He was completely insane and obsessed with a fashion model, enough to kidnap her on her wedding night, declare the marriage a sham, and immediately spill his intent to force the model into his own marriage, have sex with her and then slit her throat followed by his own suicide. His house was in the middle of nowhere with all windows sealed by glass building blocks painted over, his only opening window wedged and no escape for his hostage. He witnessed his mother's murder and subsequent suicide of his own father as a child, which no doubt led to serious mental trauma. His only goal was to marry a woman and slit her and his own throats in the same manner! He also does many things that are far beyond creepy. It does not help that he is a certified medical student.
He may have been pretty bad, but probably doesn't come close to Joe Devlin, his son, the O'Connell family or the rest of the IRA terrorist bunch from The Conspirators. We're talking about a terrorist cell that was operating in the US under the guise of an anti-terror peace group, claiming to raise money to help end the violence, only to use the money they raised to buy guns which they sent to Ireland.
The very first killer, Dr. Ray Flemming in "Prescription: Murder," is a Faux Affably Evil psychopath who brutally murders his wife simply because he's tired of being married to her, manipulates his friends and his patients into helping him cover up his role, and seems to take a sadistic delight in rubbing Columbo's nose in his inability to prove his guilt. Really, one of the few killers on the show to just have no redeeming qualities whatsoever.
Harold Van Wick from Playback is an egocentric inventor, who married a wheelchair-bound woman hopelessly in love with him and so took over her role in her mother's company. He was a sub-par businessman only tolerated because of his wife's love, and he cheated on the wife with several women while pretending to be very much in love with her. He then murdered her loving mother because she was about to fire him. Also, he almost threw a tantrum at the very mention that his wife might take an active part in running the company and put him in a subservient position to his own wife.
"Funny Aneurysm" Moment: Throughout the series, Columbo expresses a severe dislike of dentists, and the few times he has to go it ends up being a total nightmare for him. It's believed that a bad reaction to drugs during a dental visit is what led to the onset of Peter Falk's dementia, the illness that killed him.
Two actors who played murder victims later became victims of actual murder- Barbara Colby("Murder By The Book") and Sal Mineo("A Case of Immunity")
Magnificent Bastard: Columbo himself, as well many of the killers (notably the ones portrayed by McGoohan and Cassidy).
The Problem with Licensed Games: In a rare example predating video games, there was a Columbo board game. The problem was, it really had little to do with the character and the only image of Columbo was a simple drawing showing him from the back, one can assume because they didn't have permission to use Peter Falk's likeness.
They Wasted a Perfectly Good Plot: "Rest in Peace, Mrs. Columbo" involved Vivian Dimitri, the ex-wife of Pete Garibaldi, a man Columbo had arrested years before, plotting to kill Columbo's wife because her husband died in prison of a heart attack, for which she blames Columbo, as well as her husband's partner Charlie Chambers. It's too bad that the case in question was never one that had been filmed as an episode, leaving us to merely guess at the exact details.
Actually, they do give us a few details: namely, the fact that Pete committed embezzlement and may have killed someone who threatened to expose this (he plea-bargained the charge to manslaughter).
The Woobie: Numerous murderers are pushed around by Asshole Victims, such as Beth from "Lady in Waiting" who is held down by her dominating brother and mother for her whole life. Once her brother is dead her life turns around and she's suddenly more assertive and in control of her life for once.