Go and tell the girl I like that I love her, of course, then depends what her reaction is after that... At some point I would basically go and get completely rat-arsed, wasted, off my face, and so on. You get the picture. Hopefully I'd be unconcious or tired out [

] by the time the end of the world actually happened, so I wouldn't die in lots of pain...
That said, I'd possibly use the opportunity to actually unleash my sadistic side, since I keep it hidden usually and limit it to an unhealthy fascination with the macabre. It would therefore be fun to actually use that side of me and unleash the fury on those I hate (they know who they are...).