re: What to do when asked to be a reference for someone you don't want to refer?

That's his fault for asking for a reference from someone from a job he wasn't good at.

If he really was as bad as you describe, he knows it, or hes an ignorant dummy. In either case, give him what he asked for. It won't be what he was expecting, but he'll never know it. He's not asking you for a letter is he, just to be a reference? Does any company ever actually call references? Especially for new people into the workforce such as this dude?