I agree on the Donald Pleasance comment. I think the writers went out of their way to write the line where pleasance says "our mother was english; she provided the breeding."
A lot of the actors/actresses listed above in the previous comments I find are all pretty good in their roles, it seems that the actual character they play is irritating rather than the performance itself. No, in my mind the worst actor award has to go to Roddy McDowall playing Roger Stanford in 'Short Fuse'. You watch the episode again - he ruins a perfectly good script with his over the top 'stage school' style of acting. The portrayal is so forced and McDowall is trying to steal each scene from the other actors, including Peter Falk. 'Short Fuse' could've have been a classic early episode in the hands of a fine actor, instead we get Roddy McDowall playing Roddy McDowall.
Mickey Spillane (Alan Mallory) in Publish or Perish wins the gold star. Second would be Frank Converse in Requiem. The dude seems thoroughly uncomfortable with his lines, and lays a brick. My god, that scene when Columbo is at Ms. Chandler's front door and Mr. Fallon (Converse) comes out to greet him should've been edited out of the show altogether.
Let's see.. Oh and all the actors in Mind Over Mayhem, except for the kid and the robot.
My vote goes to Leonard Nimoy in A Stitch in Crime, his performance makes me cringe so much I almost can't watch that episode. Especially when the character goes into a fit of giggling when Columbo accuses him of planning to kill Dr. Heidemann and warns him that he'll have to take very good care of him. Both that scene and his acting pretty much throughout the episode (including the Vulcan death grip he uses to fell Harry Alexander) are SO forced.
BTW I'll never understand why this episode isn't slated more than Dagger of the Mind, I actually find the latter very enjoyable!
sorry...I'm somewhat new to site and reviewing some rather old posts....but am loving the detail of those said posts
as for worst actor/actress...the difference between Ray Milland's two appearances is night and day...fantastic in Death Lends a Hand and lame lame lame in Greenhouse.
My fellow Canadian Larry Mann's performance...Albert... in Murder Under Glass was very wooden I thought.
other mentions
Shirley Blaine..Lovely but Lethal
Ruth Stafford (Collin Wilcox)...Exercise in Fatality
Lewis Lacey ..(Darrell Zwerling)...Exercise in Fatality
the boy genius...Mayhem
Janie Brandt ...Jeannie Berlin ...Old Fashioned Murder