Take my advice...I don't use it anyway SPECIAL EDITION: If you're feeling shit then this will make it worse

EAT EVERYTHING IN SIGHT!
This is a sure fire way in making sure that you hate yourself.  You may even consider sticking your finger down your throat after you have inhaled the family size instant mac and cheese followed by 2 mars bars and it's probably not a bad idea.  I mean, vomiting and over eating whilst crying is the ideal way to make yourself feel better when you're going through a fuck show.

TEXT/MESSAGE/FB/TWEET THE DUDE THAT HAS ONLY EVER MADE YOU AN OPTION.
It will be even WORSE if he doesn't reply.  Here you go, why don't you just take this knife and make a few wounds on your arm and then I'll just pour all this salt in them?

YOU SHOULD GOSSIP AND TALK SHIT ABOUT EVERYONE. 
I mean, when you are feeling lonely and a bit down, the best thing to do is to start alienating and stabbing all your friends in the back.  You will feel like such a champion for doing it so why not take it a step further and flirt with their boyfriends?

YOU SHOULD HAVE LOADS OF MEANINGLESS, UNPROTECTED SEX WITH BONEHEADS. 
It just does wonders for the soul and self esteem.  Nothing quite says 'I love myself' like getting naked with someone that probably can't remember your name and convinces you that using a condom is a silly idea.  Why not take some naked photos of yourself with your head in smiling and waving and send it to his phone AND email just in case he didn't get it?

SPEND ALL YOUR MONEY ON JUNK AND/OR BOOZE AND DRUGS.
Because the anxiety of not being able to pay rent and your phone bill and the impending sense of doom one gets when they are having financial problems will far out weigh any troubles that are going on in your world innit?

DON'T CLEAN THE HOUSE OR DO ANY LAUNDRY FOR AGES.
It's great to just sit in squalor and look shit as well as feel shit. You want to be authentically shit inside and out hey?  It's awesome when you open the fridge and it smells like somebody's cat died in there, you just feel like you are in complete control of your life. All good, nothing to see here!