to be explicitly drunk; inebriated
origin: sheets actually refer to the
ropes that are used to secure a
ship's sail. If the 3 ropes used were loose in the wind, the sail would flop around, causing the ship to wobble around, much like a drunk.
Margo was three sheets to the wind by the time
we made it to
Doug's party, judging by her inability to keep her clothes on.