Whoa There Almost Homeless Guy

Rather than sitting him down to "have a talk", just initiate each step.

Applying for a credit card that you co-sign on is a big improvement. Have him chuck the gas bill on it and have him pay you each time he uses it. Check it every day and ask him for the money when he uses it.

This way, he can get his own card on his own line, when he doesn't live with you.

After that, start having sex, really loud on a regular basis and start being generally annoying, without directing it at him.

Start wearing underwear and socks around the house, cut down on cooking and stocking the fridge, leave the TV on relatively loud, etc. Don't fight his resistance. Just keep doing it and find your own ways to be a pest, in general. Ask him to do errands. Ask him to buy you milk and bananas, ask him to buy you cigarettes if you smoke, go into his room and clean it and put things wherever you see fit without it being terribly crazy. Just moving their stuff will drive them nuts.

Listen to annoying music that you know he hates and repeat it. Don't be a jerk, just be liberal with doing things that get on his nerves.