Kenny Shopsin complained bitterly to me a couple of weeks ago about the fact that no food writer had sampled his sliders, which he proclaimed to be the best in NYC. So last Friday I braved the sweltering heat and went down to Shopsin's for the sliders, which come three to an order accompanied by Shopsin's very good fries. Damned if Kenny wasn't right. His sliders were magnificent: each mini-burger had a crunchy exterior and was juicy inside, crunchy yet pliant fried onions were actually melded into the top of each slider, along with American cheese. The mini-potato buns were grilled and buttered, so they formed a snug holder for the burgers. The bad news is that Shopsin's is now closed for a month for vacation. But his movie "I Like Killing Flies" opens this Friday at the Cinema Village.