Severely intoxicated from alcohol, to the point of finding control of one's actions or coordination difficult. Taken most likely from nautical terminology, in which a "sheet" is the rope that controls the sails of a tall ship; if several sheets are loose or mishandled, the boat's movement becomes unsteady and difficult to control, like that of a drunk person. On his 21st birthday, Jeff's friends took him to every bar in town until he was both sheets in the wind.