http://www.livescience.com/technology/destroy_earth_mp.html

Well, it's not so easy !

i like this one :

no1 Hurled into the Sun

You will need: Earthmoving equipment

Method: Hurl the Earth into the Sun. Sending Earth on a collision course with the Sun is not as easy as one might think; even though you don't actually have to literally hit the Sun (send the Earth near enough to the Sun (within the Roche limit), and tidal forces will tear it apart), it's surprisingly easy to end up with Earth in a loopy elliptical orbit which merely roasts it for four months in every eight. But careful planning can avoid this.

This is impossible at our current technological level, but will be possible one day, I'm certain. In the meantime, may happen by freak accident if something comes out of nowhere and randomly knocks Earth in precisely the right direction. Earth's final resting place: a small globule of vaporized iron sinking slowly into the heart of the Sun.

Earliest feasible completion date: Via act of God: 25 years' time. Any earlier and we'd have already spotted the asteroid in question. Via human intervention: given the current level of expansion of space technology, 2250 at best.

i like this one too

no6 Destroyed by vacuum energy detonation

You will need: a light bulb

Method: This is a fun one. Contemporary scientific theories tell us that what we may see as vacuum is only vacuum on average, and actually thriving with vast amounts of particles and antiparticles constantly appearing and then annihilating each other. It also suggests that the volume of space enclosed by a light bulb contains enough vacuum energy to boil every ocean in the world. Therefore, vacuum energy could prove to be the most abundant energy source of any kind. Which is where you come in. All you need to do is figure out how to extract this energy and harness it in some kind of power plant - this can easily be done without arousing too much suspicion - then surreptitiously allow the reaction to run out of control. The resulting release of energy would easily be enough to annihilate all of planet Earth and probably the Sun too.

Slightly possible.