Here is an exact response we gave a couple the other day. I'd be curious to see what everyone thinks.
"Hey, sorry it took us a day to get back to you. We did get a chance to talk last night and look at your profile. You are both attractive but we just didn't feel the initial connection to move to the next step - maybe you felt the same after we opened our pictures
Thank you very much for your consideration of XxxxX and I and maybe we will catch you at a social sometime. Thanks. XxxxX & XxxxX"
Since you are meeting them at a social then you might want to reword it with we would love to chat with you at the social and meet new friends in the lifestyle, etc but this is our typical thanks but no thanks.