“The door’s on the other side of the building, young warrior and pesky quarry. Or do your rebellious kind always both escape and enter by windows?” a smooth deep voice rolled.
...
Mythron’s eyes gleamed. His eyes were convincing, too. “Normally they save the ‘I won’t talk’ stage until later in the proceedings, but we might as well skip to that part, scum. Now that we’re at that part of the investigation, I’ll do the usual and…” he paused, quickly unsheathing his sword and placing it against Terin’s neck while stepping on Terin’s outsretched arm, “and apply deadly force. Talk.”
...
As Terin kept silent Mythron sent his gaze straight into Terin’s eyes and pressed the sword harder. The hands were experienced at pushing just hard enough, but not so far to kill. “Talk.”
“It is lovely weather we are having.”
“Oh, I forgot about the sarcastic stage. Silly me. Generally chopping of the right hand ends that part.” Mythron raised his blade, clearly ready to abide by his threat.

What do you all think of humorous and amusing villains? Have you written any into your books, or remember any from books you've read or movies you've watched? Do you think these types of villains are effective? Does it make a difference if the normally-dark-and-creepy overlord just has a comedic slip-up, versus a repeatedly goofy character?

The best example I can think of off the top of my head is Jatt & Jutt from the Legend of the Guardians film. These two minor bad guys are constantly teasing each other. You get the impression that they get along well as brothers, and a lot of their one-liners make the audience laugh.

My problem with this is that, when a villain is repeatedly funny, they aren't scary any more. I have a hard time taking them seriously, and they don't feel like much of a threat. This weakens their power as bad guys, I think. An occasional comedic slip-up would be different - everyone has their embarrassing moments.

What do you all think?

I like sarcastic villains, so long as they are still ruthless, scary villains. If they are too funny, you don't respect them as villains.

One of my stories though, The Dying Words of Dick Eldin, Galactic Gumshoe, has a surreal, almost Cubist feel similar Lewis Carrol's Alice in Wonderland where the villain, nay, everyone is bizarre, illogical, and somewhat funny.

In the last case, he has to be funny, or somewhat funny (He's a Mafia Don named Don) to add to the feel of the story.