A father was charged early Sunday morning with violating the Suffolk County Social Host law after hosting what police called a “post-prom gathering” for his son at his Amagansett house. East Hampton Town police said teenagers were found there drinking alcohol.Capt. Chris Anderson said Tuesday that more than 40 teens, the majority of them students at the Ross School, were in attendance at the party.At about 12:50 a.m., Arthur W. Bijur, 62, called an ambulance to his house on Acorn Place for an unconscious boy who had reportedly drunk too much. Police responded along with the Amagansett Fire Department and found “obvious signs of alcohol used by minors, and intoxicated youths,” Captain Anderson said. The boy was taken to Southampton Hospital, and the party was shut down.Mr. Bijur was given an appearance ticket citing violation of the Social Host law, an unclassified misdemeanor. The law prohibits adults from knowingly allowing the consumption of alcohol in a residence by a minor.