Things that ensure their defeat, such as Homer Simpson's "No comeuppance. NO COMEUPPANCE!!!!"

Mine is:

"He's only one man. What can he possibly do?"

"I'll get you my pretty and your little dog too"

"I'm going to count down from ten, and when I get to zero, I'll say 'Now!', and I'm going to shoot you! So don't even think about ducking, or moving out of the way, or anything like that! Are you ready? Ten.......nine......"

"You'll never catch me"

They usually catch them.

"I'm just going to give this up and grow flowers."

Anything with the phrase "master plan."

"Bring him to me alive. I'll deal with him myself."

I like the old "I'd like to kill you myself, but I've got pressing engagements elsewhere, so I'll leave my henchmen/traps/lasers/attack dogs/etc. to deal with you instead."

So instead of taking the 5 seconds it would take to walk over to the helpless hero and shoot him in the head, he leaves, and before whatever the villian has left behind can take care of the hero, he finds someway to escape and thwart the villian.

" I'm going to kill you anyway, so I might as well tell you..."

A good hearty, maniacal laugh always seems to be a bad idea...

And trying to get the good guy to join 'em never seems to be a good idea. Everyone remember what happened in Conan the Barbarian? Ahahaha...

Somehow, reverse psychology seems to be their best bet at stayin' alive. "Come on, pull the trigger, kill me, yada yada..."

"Prepare To Die!"

(Giving the hero time to think out his escape!)

"...and I would've got away with it too if it weren't for those meddling kids!!"

They should never monologue.

"Oh, ho ho! You sly dog! You caught me monologuing!" --- Syndrome

Refer to the overlord list.

I was wondering where that was! A friend of mine showed it to me a couple of years ago and I had forgotten it existed.

I like the one about: "He is just one man, what can he possibly do?" Then the bad guy says: "This" (takes gun and shoots henchman.)

I'll be back

"oh so you didnt tell him"- Kevin Spacey- SEVEN

Wow! I almost forgot about that list. It's still hilarious!

As an aside, I HATE it in every film when the bad guy goes into his "We're not so different, you and I..." speech. Do screenwriters think this has never been done before? Good Lord.

There will be no one to stop us this time!

And the corollary, when his nemesis is discovered to be within his lair:

I must face him...alone!

You just don't get it do you Scott?

I was thinking the same thing.

Now let us resume the unnecessarily slow-moving dipping mechanism...

Heh, I was watching XXX: State of the Union a few nights ago, and the main bad guy uses pretty much this exact quote towards the end of the movie.

Twirling moustache.