A phrase used by Holden Caulfield, of The Catcher in the Rye.

When he's discussing his crush, Jane Gallagher, he calls her sorta "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. That killed me.

It's also something I had to battle all through high school. Good thing there's a term for it, not a catchall like "stutter."