Most dread inducing phrase a GM can speak?

[GammaPaladin]

What do you think are the most terrifying words a GM can say when running a game?

Personally I think Champions has the most terrifying possibility:
"Combat phase one. Villain acts."

[Mr. Friendly]

*arbitrary die rolls behind screen*
*big smile*
"You are absolutely certain that your meal isn't poisoned"
*bigger smile*

[Duke of URL]

"Everybody, tell me exactly where your character is and what he's doing, and roll initiative."

[Darkantra]

"For this game my NPCs can use the diplomacy rules on you."

[Ascension]

I personally think "Make a spot/listen check." followed by silence is the worst thing you can hear... or rather, not hear, as the case may be.

[SamTheCleric]

"Roll for initiative."

[Sofaking]

"For this game my NPCs can use the diplomacy rules on you."

HAHA! QFT!

[LongVin]

"Hey, can you roll your <skill> for me?"
*rolls* "I got a <number>. Why?"
"hmm...Don't worry about it."
"Uh..what was the roll for?"
"Don't worry it's not important." *DM makes some rolls*

[elliott20]

"hey guys, I just got these new books with these new rules in them. I so wanna give them a try"

[Hadrian_Emrys]

I don't think my players ever really listened to me after the first session I ran. They just stared REALLY hard at my face, looking for signs of a sadistic look in my eye or that subtle lift on the right side of my mouth. Something like this actually:

[Xuincherguixe]

"For the next part of the game, there will be no violence."

[Mauril Everleaf]

This one was from a session just a few days ago.
"Heh, if you screw this up, you are going to hate me."
This was followed by the characters bickering behind a door for 6 rounds.

The second worst was from the last session: "You weren't supposed to have killed him..." It was the commander of our cleric's army.

[Lairship]

"The dragon is in season."

[Armoury99]

Personally I'd go with the "are you sure?" question that tradditionally means 'you're insane, but now at least I've warned you' - the dread is usually confined to other PCs in the (sometimes literal) blast radius.

I also regularly borrow my favourite quote from Knights of the Dinner Table, which is "Saving throws are a crutch for the weak." (thank you Wierd Pete)

My all time favourite from a player-point of view was when I was playing Elric! a few years ago, with a GM who brings new meaning to the words Low Fantasy. Having stolen cabbages to survive in a previous game, he was keen to point out that his new campaign would be more High Fantasy... After one of the characters ended up in prison for a few weeks he proudly proclaimed his High Fantasy credencials by saying: "I didn't even roll to see if the guards sexually abused you during your stay."

And he was being serious.

[Azerian Kelimon]

Of course, the worst thing to hear actually isn't heard. Rather, it's seen: A Gigantic Cheshire Cat smile. While a sadistic smile tells you that it's gonna hurt, the cheshire cat smile tells you the DM is planning something truly malevolent.

[gm_rand]

“Hmm I'm out of minatures and have used all my dice as well. I'll be right back with some tin foil.”

[Telonius]

I'll second "Are you sure?"

"Does anyone have any extra minis?" is a close second.

[The Rose Dragon]

"You win the game. Congratulations."

That evokes the following reaction from the players:

"You mean we'll have to wait until you prepare a new game? That sucks."

[Ganurath]

"Make a Bluff check."
"Hah! I rolled a 19!"
"..."
"What?"
"..."
"WHAT IS IT?"

[Glawackus]

Really, 'roll for initiative' is pretty hard to beat.

[Sir Enigma]

"Well, that's amusing" after making dice rolls

[Ganurath]

Really, 'roll for initiative' is pretty hard to beat.

"I'm sick."

[The Gilded Duke]

In this situation I'm going to house rule that...

-

I really hate unannounced and undocumented house rules, especially ones made up on the fly. I think that it is one of the worst things that can happen in a game.

[Sstoopidtallkid]

"Oops", during combat, right after a NPC gave a prophecy that the one currently fighting had to be present at a certain event in order to save the world, was pretty dread-inducing. (turned out, he'd just critted and rolled 98 on the percentiles to confirm. Not fun)

[Number 6]

This is Shirley, our new player. She's also my girlfreind.

[Rutee]

"The DM's girlfriend" isn't really that bad. Though I'm used to Nerd Couples so there you go.

I'm going to say, in general terms, that big grins are the worst communication signals a GM can ever give. In specific game terms, well.

"Let me explain to you about the Kukla.."

[Duke of URL]

This is Shirley, our new player. She's also my girlfreind.

You win the thread.

[Ecalsneerg]

It's not really a phase, but my DM has two tubs of figures. One is the 'safe' Malteasers tub, containing Medium/Small critters. We use it every session, due to general low-levelness.

So, we're in trouble when the whisky container of Large upwards figures comes out...

[sonofzeal]

DM-who-strongly-believes-in-dice-mojo: "*eye twitch* Hang on, I'm going to need my pewters for this."

[Squash Monster]

That gives me an idea.