Quote Originally Posted by beachguy in thongs
three sheets to/in the wind Informal
Intoxicated; drunk.

A sheet in the wind
half drunk.

be three sheets to the wind (old-fashioned)
to be drunk. Bobby was already three sheets to the wind when we arrived.
I explained before, also it's like on a ship, when the sheets were let loose (let to the wind) the boat would stagger and sway. like a drunk.
So it's an expression for being really drunk.