What's the best way to let a guy down?

What are the best ways to let someone know you're not interested? I'm not talking about breaking up with someone you've been going out with for months. This is a just a step or two after the first time you meet someone and know right off there's nothing there.

This is what you say to someone after seeing them a time or two. You've spent just enough time with him to see the red flags pop out. Maybe he talks too much about himself. Even if it's interesting talk, I say it's a deal breaker. Then he's the guy that turns into an animal the first moment you're alone together. To many hands!

So what do you say when they call and text about wanting to go out again? I try being busy and hope if I'm busy long enough they'll give up. But my bad date from a few weeks ago kept coming back. I was busy at least three weekends in a row and it didn't seem to matter. He kept coming back.

I want back and forth on what to say. Should I tell him I'm seeing someone else? I kind of am, but is it really any of his business? My friend pointed out that he might get the wrong idea. Considering his ego, he would think if I hadn't picked the other guy I would've picked him, As I told my friend, I would rather spend every night in my apartment with Lucy than with him.

I don't want to be too vague or too bitchy or too passive. So what do you say to end it before it starts?  

Love to the single girls,
Addison