It seems that people are being denied for no reason at all-- we know this because plenty of these people are approved after an appeal or talking to a supervisor. Personally, I'd file a complaint with the DHS OIG in addition to a FOIA request and an appeal. I'd also file a TRIP application. You might drum up more attention by raising the concern that your interviewer's demeanor changed when he found out you are gay. It probably isn't the reason for your denial, but it might make them look into it faster because it has a discrimination aspect to it.