three sheets to the wind

Also, three sheets in the wind. Drunk, inebriated, as in After six beers he's three sheets to the wind. This expression is generally thought to refer to the sheet-that is, a rope or chain-that holds one or both lower corners of a sail. If the sheet is allowed to go slack in the wind, the sail flaps about and the boat is tossed about much as a drunk staggers. Having three sheets loose would presumably make the situation all the worse. Another explanation holds that with two or four sheets to the wind the boat is balanced, whereas with three it is not. [Mid-1800s]

Very drunk. Despite what it sounds like to nonsailors, a “sheet” isn't a sail. It's the rope that secures the sail's edge or corner to the mast or the vessel itself. A sheet that comes loose flaps erratically, much like a drunken sailor weaving his way back to the ship after a night's alcoholic revelry. Three sheets blowing in the wind would be even worse.