1: The universe's insane asylum. Current inmates: Homo Sapiens. Everything else is just innocent. Nature is our jailkeeper.
3*: Mostly Harmless
4*: Computer designed to figure out the ultimate question of life, the universe and everything
5: Only planet in the system of Sol capable of sustaining life.
7: A rathole being killed by its scourge: intelligent life
Note that definitions # 3 and 4 are from The Hitchiker's Guide to the Galaxy.
Earth is the most horrendous place in the galaxy, and it houses the most fucked-in-the-head species in the universe. Good luck in hell, fuckers.