That is, actually destroy the physical earth, as opposed to merely making it uninhabitable. It turns out to be a) quite a difficult task to achieve in reasonable time, but of course b) a very easy task if you have an awful lot of patience.
My favourite methods:
- Destroyed by vacuum energy detonation (you will need: a lightbulb)
- Engulfed in supernova (“…one of the most efficient and spectacular ways to destroy the Earth, so if you have the necessary skills and machinery, then I would recommend this over most other methods.”)