Everyone knows that a very few killers are ready to actually harm Columbo in the final scene if they can, like Eric Mason and Beth Chadwick. But there must be a few others who seem a little unpredictable when it comes to that (even if the viewer knows it won't happen, it being a COLUMBO episode).
The one I always think of is Harold Van Wyck. He practically explodes, then of course he controls himself completely and makes that little gesture about that to the uniform cops.
There must be a few others who don't follow the COLUMBO "pattern" of being calm at the end, but I can't really think of them.
Viveca Scott, while cool on the outside, was obviously fuming on the inside.
Paul Gerard in Murder Under Glass was planning on killing him.
Milo Janus might have been fired up enough to try.
Fielding Chase was getting a shotgun right at the end of Butterflies in Shades of Gray. I truly believe he would have offed Columbo.
Vivian trying to poison Columbo with the marmalade in "Rest in Peace, Mrs. Columbo".....Columbo lets her think she is getting revenge and lets her confess before springing the news that his wife is still alive. She end up slapping Columbo as her emotions did a quick 180.
Doctor Bart Kepple seems to have something of a break down at the end. He starts of with the confident "without my help you would have never solved it" before breaking into a chuckle and then a laugh but by the freeze frame his expresion is rather manic. I could well imagine he jumped up and tried to attack Columbo.
"Junior" is very unpredictable when they're on the tram going up to pinewild. He thought there was a bomb in the cigar box, he was capable of anything. At one point he even opens the tram door.
Note: last month during the holiday season I heard an old, classic Christmas episode on the radio starring Roddy McDowall. Who was very very young at the time. I believe the date was sometime in the 1950s.