Rip off the bandaid
On more than one occasion I hear "I don't want him to think I'm a douche" and "I don't want him to think I'm a bad guy" from D. I counteract that by saying D is being a douche because he's leading APB on.
Clearly D has no interest in APB, but he raises the hopes of APB by quickly replying to texts, answering calls and making up excuses about how he's "happy being single" and "not really into dating right now." Those are motivators for those who are agressive and who pounce given the chance.
From my experience, it's just easier and less painful to rip off the bandaid quickly. Sure it will sting, but only for a few seconds. Why let the wound fester? Cutting off the limb is the quickest way to stop the virus from spreading.
In the end, I tell him he's a grown man and will have to deal with whatever consequences that transpire from his inability to be upfront and tell APB he's not into him.
I doubt he listened to my advice since he met APB for drinks a few nights later...