Ok, so, you're evil and going to kill everything, we get that

[Evil Earlgrey]

After that the real, gray and boring button will appear. Pressing it will up the oxygen content of the athmosphere by 500 000% immidiately. This will result in horrible things really quickly.

I am happy to inform you that even a 100% oxygen atmosphere is not going to kill humans, altough they might need to periodically breathe a closed breathing loop with an co2 scrubber in the longrun to give the lungs a break.
Because the Atmosphere is not a closed space, the increase to a partial pressure of 1050 bar will probably result in a massive volumetric increase of the atmosphere, but not likely in a much higher pressure. Haven't done the calculations on that one, but even an oxygen pressure increase by 760% is not problematic for humans.
Now if you increased the pressure of nitrogen, THAT would have more interesting effects (like everybody beeing high).

Yeah i know.. i just felt the need to point that out.

 

[NathLines]

Mine is divided into two parts. The first part is a button that start a random fire in the house. The second part is the pin of the fire extinguisher labeled "In case of small fires and world destruction".

If some hero-dude came and killed me after I pressed the first button, he might try and put the flames out with the extinguisher... Assuming he can't read that is. Or if he shoots the extinguisher it might be become really cold and hard to breath, I dunno...

 

[Firoth]

After that the real, gray and boring button will appear. Pressing it will up the oxygen content of the athmosphere by 500 000% immidiately. This will result in horrible things really quickly.

I am happy to inform you that even a 100% oxygen atmosphere is not going to kill humans, altough they might need to periodically breathe a closed breathing loop with an co2 scrubber in the longrun to give the lungs a break.
Because the Atmosphere is not a closed space, the increase to a partial pressure of 1050 bar will probably result in a massive volumetric increase of the atmosphere, but not likely in a much higher pressure. Haven't done the calculations on that one, but even an oxygen pressure increase by 760% is not problematic for humans.
Now if you increased the pressure of nitrogen, THAT would have more interesting effects (like everybody beeing high).

Yeah i know.. i just felt the need to point that out.

Wouldn't the whole world ignite once that high oxygen content hit a bug zapper or some open flame?

 

[Kranay]

Mine's in the shape of a phallus. Because to blow up the world, I'd have to be a real dick.

 

[KarumaK]

It's a bright yellow awesome face residing in my imagination,

It does whatever I happen to want it to do at the time when pressed.

 

[Space Spoons]

Mine is actually a lever. A yellow lever with a smiley face on it. This lever:

I like there to be an element on chance in my doomsday scenarios. Maybe I'll destroy the world as we know it, maybe I won't. Pig goes oink... Everyone gets a Grand Slam from Denny's, and I'll foot the bill. Cow goes moo... I drop a thermonuclear bomb into the planet's core.

And really, when the big hero busts into my lair, what's he more likely to suspect; my big powerful supercomputer, or that See-n-Say in the corner?

 

[LeonLethality]

I don't have a button, instead my plan goes into action when I wink with my right eye.

What if you get dirt in your eye and wink by accident?

OT: Red round button with a smiley face.

 

[joshuaayt]

I'll have a fake button, that I'll always keep on me- a big red one, with cool things attached. Then when the heroes knock it out of my hands, I'll be all
"... It doesn't matter. I am a cautious man, Freedom Force. Did you think I would allow you to stop me so easily? Did you think I would design my beautiful machine to be reliant on a human, pathetic as we are?
No... Do you understand yet?
Your world... your precious Earth... ALREADY, SHE BURNS!"
And then they'd be all
"OH NO!"

 

[Bealzibob]

I don't even remember anymore. After my evil loses from the stockmarket crash, my evil desk has been so swamped with evil documents and even eviler tax claims, I havn't had neither the time nor the finacial footing to create any evil plans.

Currently, I'm just working on a evil plan to not get evicted out of my evil lair and keep mutation injects on the table from my evil super-soldiers. After Shego left me I just don't have it in me anymore.

Anyway, I'm sure it was just a decent sized red button, something practical.

 

[QCX]

I have a button that will convince everyone that the person next to them is actually Adrian Brody and that he will kill them, if they do not first kill him.

The button is is around 10cm in diameter and is brightly coloured red with the word "Dun" written on it.

If the world does not surrender to my will and give me ten bagillion dollars and a picture of myself engraved on the moon, I will press the button.

 

[RelexCryo]

Fist sized, cherry red, glass cover, labled STFU.

Mine will be big, red, and labeled "SELF DESTRUCT BASE."

The hero will wind up destroying the everything. Heh.

 

[C95J]

my button is on the roof of my mouth, where no one can find it mwahahahaha!

 

[SL33TBL1ND]

Mine would actually be more of a switch that said "Magic" on one side and "More Magic" on the other.

 

[Shemming]

I giant red shiny button..... that can only be activated by headbutting it with my exact head print, this is solely there for when my plan eventually fails i have a excuse to facedesk.

 

[sylekage]

My button is on my person at all times. Where you ask? In my nose. If i ever need to press said button, all I have to do is "pick" my nose. This is very troublesome, at times, when I actually do have to pick my nose. Remember hurricane Katrina? Yeah sorry, massive booger.

 

[DefunctTheory]

A button with this picture stamped into it.

 

[Mr Pantomime]

Mine is a persons eye. and when you press it its all squishy. Thatd put people off

 

[smurf_you]

Mine would be in the shape of a drunk gay guy eyeing you from across the bar..... HAHA



But no really.... it'd be like a chip in my arm or something that I'd have to tap in the exact right sequence to make it go off....

 

[Roofstone]

On the console conected to my (no, not gaminc console) doomsday machine-Sparkling with electricity of course-. There is many buttons, but one stands out.

It is the large, circular red one. In the middle, slightly up and to the right.

There is no way to activate it exept laughing an evil laugh, lifting your hand high up. Before pushing it down with all your might!