IM HERE, I WAS SLEEPING! But yeah, its not a Glasgow smile. its a Chelsea smile. You cut from one side of the lip to your ear on both sides, pour salt in the wound and make them scream in pain. Only thing violent thing that has the tag 'Glasgow' i can think of is a "Glasgow kiss". Which in short is just headbuttin' someone.
i have seen both the "glasgow smile" and "chelsea grin" phrases used, although I have heard the"glasgow smile" used a little more frequently but it could have started in either place. if you haven't heard of the black dahlia you should look her up, she had this ---- done to her and then she was cut in half. there are even pictures!