A couple thoughts - I'd be very cautious about 1) varying from your standard practice for evaluating applications ("Rather than spend time and expense of doing a full credit review...")and open the door for the applicant to allege disparate treatment on a prohibited basis; 2) using "undiserable character" unless the applicant is the well-known head of the local Mafia (assuming you don't lend to other Mafioso); and 3) varying from your procedure for providing adverse action notices (if don't provide reasons - ok; however, if you do provide reasons, it may be a "red flag" to send a one-off "no reason" denial).
Barring the applicant being the head of the Mafia, IMO, I'd recommend underwriting the request - ideally, the undisirable character will correlate to bad credit, inability to prove (or inadequate) income or inadequate collateral.
Merely my opinion...