One of the worst must be Elstree: Terrible runway surface, nowhere to park, over-controlling and bolshy (sp?) AFISO, and no circuits unless you pay Cabair's exorbitant rates or fly with Firecrest. (Yes I do know all the arguments about the NIMBYs having a very strong voice locally).
That airfield could be a goldmine if properly managed: Good location for London, lights and a hard runway, and a relatively affluent population in the area. But the owners make no attempt to improve the facilities or make it a pleasure to visit. You do well to pass through without your aircraft getting hangar rash on the apron or your ears burnt by Bossyboots. Give it a miss unless you really have to be in that part of Hertfordshire.