A "Thousand Mile Smile" is the smile you get when you are really high. It just happens, and it makes you look so stupid. Everyone around you will make fun of you for it. It will begin to hurt your cheeks after a while, but don't fight it. It's part of the fun.
A method used by London gangsters to scar up their victims. A cut is made at the edge of both sides of the mouth then the victim is kicked in the groin very hard. As he screams the flesh on both cheeks are ripped apart leaving terrible scaring.