I obviously live in a different working world than do those DUmmies ... assuming any of them actually have jobs. As job qualifications go, those are pretty minimal. I could detail why those characteristics are necessary for a cafe', but y'all understand as well or better than I do, and DU-onlurkers would refuse to understand.
I suspect the cafe's sign is a sort of pre-sort, driving off flakes and whiners without the owner or manager ever having to meet them.
WRT DUpipo, I wonder how many of them routinely complain if their order takes 5 minutes longer than they think it should ... or whine when the server doesn't check them out regularly enough due to being short-staffed ... or is horrified when a server is too chummy and familiar ... etc., etc., etc.. I suspect that when some DUpipo walk into a restaurant the servers draw straws to see who has to wait on them ... and the DUmmies leave a minimal tip for excellent service.