Why not ask why?
One of the most common responses to my turning a guy down is some form of "But why?"
This is vastly understandable and incredibly pointless, and it drives me completely bugfuck. In my long experience, this response has never gotten me or any of my friends to change our minds about fucking a guy.
Now, obviously, the urge to ask why is driven by two things:
First, you want to know what it is about you that wasn't appealing so that you know about it for the future. As we all know, I am strongly in favor of self-knowledge and growth, so this is admirable. However, it's important to recognize when and where's it's appropriate to gather such life lessons. Unfortunately, though they may be a wealth of knowledge and/or insight, women who have just declined your advances are not a good bet for this.
Second, you hope that she'll say something that indicates that she's got you wrong, so you'll be able to talk her out of it and into you. I'm sure you won't be surprised to know that this is, by far, the more common approach, and the one that I really, really hate. It makes the guy look at least a bit (in the best case scenario) desperate and it puts me in the awkward position of having to either harsh on a guy ("Your photo makes you look like a wildebeast," or "You obviously couldn't eat pussy to save your life.") or tell him that I don't have any particular reason not to sleep with him, but I still don't want to. Since I don't think I need a reason to decide not to sleep with someone, this annoys me.
It's a sad but true fact that guys who don't try to talk a woman into changing her mind definitely won't get any from her, since she's already decided no, but at the very least, she won't be posting to her blog about how sad and desperate you were when she turned you down. Save yourself the trouble, guys, and skip that part of the conversation, because it surely will not get you anywhere fun.

Comments
I think when any of us gets asked that question upon rejection, we should simply point them to your post here. If that would be ok with you. ;)
Posted by: ghislaine | January 11, 2006 10:59 AM
ghislaine: I would be very happy for people to do that!
Posted by: ClueChick | January 11, 2006 11:24 AM
Funny thing is, almost no one I reject ever asks why. Which is too bad because, busy body that I am, I'm actually hot to tell them. I used to include some sort of "why" in my rejection but all I ever got out of that was defensive flames, so I quit. But I'm waiting for the day some guy actually *wants* feedback.
But then, I'm a Certified Bitch.
Posted by: sapiophile | January 11, 2006 12:49 PM
you're merely telling how it is sapiophile, so save yourself the compliment, you ain't no bitch, you a puppy i like to spank!
Posted by: jitter | January 12, 2006 4:41 AM
jitter: if you ever want me to tell you why you are uninteresting and unattractive, let me know, I'd be glad to.
Posted by: sapiophile | January 12, 2006 12:46 PM