Abberforth of Shadow Council offered up a "Basic Assumption and Discernment System. this handy, though tongue-in-cheek guide to selecting members for a PUG. He uses simple assumptions in a players initial presentation of self to determine if a player is a good candidate for invitation. These guidlines warn players to be cautious of Elves, Death Knights, and folks with untypable or unintelligible names.
Remember that this guide is for amusement only. There are several other factors that go into good PUG players- like do they run into Nexus when you invite them for Occulus?