Destroying the Earth is harder than you may have been led to believe.
You've seen the action movies where the bad guy threatens to destroy the Earth. You've heard people on the news claiming that the next nuclear war or cutting down rainforests or persisting in releasing hideous quantities of pollution into the atmosphere threatens to end the world.
The Earth is built to last. It is a 4,550,000,000-year-old, 5,973,600,000,000,000,000,000-tonne ball of iron. It has taken more devastating asteroid hits in its lifetime than you've had hot dinners, and lo, it still orbits merrily. So my first piece of advice to you, dear would-be Earth-destroyer, is: do NOT think this will be easy.
He also warns that he can not guarantee that any of the methods he suggests will wipe out mankind, so if that's your real aim, you should go straight for it and skip destroying the Earth.
But if destroying the earth is what you want, this is the place to go.