1. Similar to motor-mouth; Someone who talks excessively to no end and about many things at once.
2. Having a crooked or eccentrically shaped mouth that is seemingly rubber-like.
"She was sort of muckle-mouthed. I mean when she was talking and she got excited about something, her mouth sort of went in about 50 directions, her lips and all."
-Holden Caulfield of Catcher in the Rye
Comes from the root word "muckled" aka being really really intoxicated.
Muckle-city relates to how people say they were "gone" last night. Well where did you "go" to my friend? After careful research the answer is MUCKLE-CITY.
It is the place your soul goes when you are black out drunk and it can't stand to see what you do to your body when you are blacked out, therefore you've GONE..to muckle-city.
"I bought a one way ticket to muckle-city last night"