Create an infestation of giant parasitic worms that digest you alive from the inside after entering through the anus, in the sewers of several major cities. Convince everyone it is a new strain of flu. Once the cities are desolate, demolish the skyscrapers. Blame it on the terrorists (pr something more creative). Humanity will have suffered a devastating,demoralizing loss, and while they are united in grief, seize the opportunity to usurp all major governments in a brilliant coup, using mostly fembots. Gradually starve my subjects until only a few remain, then use them as starting points for my new army of intergalactic mutant frogs. Once that is complete, march them to R'lyeh, a hold Cthulhu ransom.
For a million bajillion fafillion dollars.