It is when someone (perhaps a Conway) has had intercourse with a sheep so much during their lifetime, that at some point when they expect the money shot all they hear is "puuuh".. hence it's gone dry - the dry horror!!
"Did you watch that new Horror movie The Killer Werewolf?"
"No, my friend told me it was just another Dry Horror film and I just can't sit through those."
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi