You know, I've been turned down by couples before with a very simple, honest "Sorry, you're not our type physically, thanks anyway", or some variant of that. If, as a single male, you find yourself insulted by that, it's probably time to evaluate why you're pursuing the lifestyle at all.
I always politely reply with something to the effect of, "No problem, thanks for your time."
I think giving a true, specific reason or two is just good manners. Any single males that are participating in the lifestyle should face and realize one important rule...
To Each Their Own...Diff'rent Strokes for Diff'rent Folks...De Gustibus non est Disputandem (In Matters of Taste there is No Dispute)...etc.
...if you can't discriminate from innocent, preferential rejection and a personal attack, it's probably time for you to get some therapy and time for the people you're corresponding with to block you.