I'm late coming to the party, but wanted to add:
You don't have to make any loan you don't want to. As long as you're not illegally discriminating, you're perfectly fine to say "No." As Adam suggested, you can use the "no reason" denial. Or you could put "undesirable character" on the "other" line where reasons are listed. On your copy of the AAN, document the heck out of it. Examiners should not have a problem with this.
P.S. I've seen this done a few times for suspected drug dealers, those that have been arrested but not convicted, etc. "Scum of the earth" is not a protected class.