My button is a huge glowing thing that reads "WORLD DESTROYER". It's in a guarded, super secret location filled with a million billion mooks and my most uberest super henchmanses. When pressed it will initiate a countdown during which you have to open it up and mess with the wires. It will also shoot flaming, sharpened turtles at you and blare out that goddamn annoying danger noise that never shuts up. After you mess with the wires, it will have some inane puzzle that requires all kinds of stupid shit to complete, like five different seemingly useless items used in a weird and improbable way while making snarky comments.
Of course, that's not the real button, but a decoy to lure in reality-challenged individuals who actually believe that I would think it's a great idea (incidentally, this location will be hinted at "accidentally" every time the idiots punch a henchman in the face).
The real button is a lot more nefarious. It's a small thing that looks like the butt of a completely ordinary screw among many others on the underside of my bed. Except not really and and the screw's actually only the key (it has microscopic markers alongside it) needed to be put into a certain other thing in a highly illogical way that cannot be deduced (and has never been seen by anyone and that only I know by memory). 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.
Alternatively, my button is a giant yellow thing with a big smily face. It will look like the cheeriest thing ever. It will say "Press me for happy fun times!" on it. Pressing it will activate a sequence that tracks down every idiotic YouTube comment's writer and then starts broadcasting their comments inside their heads so loud they cannot think. If the "victim" (I'm at loath to use this word to describe the recipients here) is still alive after hearing his own retardation for two days, the broadcast will go vocal and actually start coming from within their heads. This will hopefully have the effect of passer-bys attempting to lynch them, either out of rage or an attempt to protect themselves.
After the button has been pressed, the effect is active forever and will also hunt down new posters. The effect may spread to include every page on the internet, depending on how things go. It will probably not kill everyone in the world, but it will improve the quality of life by at least 1500%