Given the relatively gloomy summer — has there been a day when it hasn’t rained? — New Yorkers have been eager to shed their layers whenever they can. But what lies beneath is no guarantee, as party hosts around town have learned in the last few months. For instance, it’s doubtful that one Upper East Side design maven expected guests to show up to her cocktail soiree spilling out of their red frocks or donning bustiers that looked as if the label read “Edward Scissorhands.” Or what about the dark winged warlock look one partygoer donned at an art benefit downtown? But surely the organizers of the Watermill Center’s annual gala knew they were asking for it. The dress code was designated “inferno,” and guests dutifully obliged, opting for a shredded twist on lederhosen, an inexplicable sports jersey and a pair of particularly unsubtle painted jeans. It can certainly be said that these shocking ensembles liven up what can be an otherwise staid social scene, but whatever happened to the sundress? That is, if the sun shines.